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Versions: (RFC 1327) 00 01 02 03 04 RFC 2156

Network Working                                             S.E. Kille
Group                                                       Isode Ltd.
INTERNET-DRAFT                                           February 1997
                                               Expires:    August 1997
                             File: draft-kille-mixer-rfc1327bis-04.txt





              MIXER (Mime Internet X.400 Enhanced Relay):

                Mapping between X.400 and RFC 822/MIME





Status of this Memo

This document is an Internet Draft.  Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups.  Note that other groups may also distribute
working documents as Internet Drafts.  Internet Drafts are draft
documents valid for a maximum of six months.  Internet Drafts may be
updated, replaced, or obsoleted by other documents at any time.  It is
not appropriate to use Internet Drafts as reference material or to
cite them other than as a ``working draft'' or ``work in progress.''
Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet
Draft.








Network Working Group                                       S.E. Kille
Internet Draft                                              Isode Ltd.
RFC 1327bis                                              February 1997
Obsoletes: RFCs 987, 1026, 1138, 1148, 1327, 1495
Updates: RFC 822


             MIXER (Mime Internet X.400 Enhanced Relay):

                Mapping between X.400 and RFC 822/MIME



Status of this Memo:

     This document describes a set of mappings which will  enable
     interworking  between  systems  operating  the  CCITT  X.400
     Recommendations on Message Handling Systems (1984, 1988  and
     1992  versions)  /  ISO  IEC  10021  Message  Oriented  Text
     Interchange Systems (MOTIS) [1,13,15], and systems using the
     RFC  822  mail  protocol  [16] or protocols derived from RFC
     822, supplemented by the  MIME  specifications  [9].   Older
     systems  which  do  not  use  MIME  are still supported. The
     approach aims to maximise the services  offered  across  the
     boundary, whilst not requiring unduly complex mappings.  The
     mappings should not require any changes to end systems. This
     document  is  a  revision  based on the evolving sequence of
     RFCs 987, 1026, 1138,  1148  and  1327  [17-21],  which   it
     obsoletes.   It  incorporates  changes specified in RFC 1495
     [4], which it also obsoletes.

     This document specifies a mapping between  two  families  of
     protocols, which includes both protocol/service mappings and
     use of a  mandatory  global  mappings.   This  specification
     should be used when this mapping is performed.

     This draft document  will be submitted to the RFC editor  as
     a  protocol  specification.   Distribution  of  this memo is
     unlimited.  Please send comments  to  the  WG  mailing  list
     <ietf-mixer@innosoft.com>.







Kille                                                         [page 1]


RFC 1327bis
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                          Table of Contents



     1          - Overview ......................................    6
     1.1        - X.400 .........................................    6
     1.2        - RFC 822 and MIME ..............................    6
     1.3        - The need for conversion .......................    7
     1.4        - General approach ..............................    7
     1.5        - Gatewaying Model ..............................    8
     1.6        - Support of X.400 (1984) .......................   11
     1.7        - X.400 (1992) ..................................   12
     1.8        - MIME ..........................................   12
     1.9        - Body Parts ....................................   12
     1.10        - Local and Global Scenarios ...................   13
     1.11        - Compatibility with previous versions .........   14
     1.12        - Aspects not covered ..........................   14
     1.13        - Subsetting ...................................   14
     1.14        - Specification Language .......................   15
     1.15        - Related Specifications .......................   15
     1.16        - Document Structure ...........................   15
     1.17        - Acknowledgements .............................   16
     2          - Service Elements ..............................   18
     2.1        - The Notion of Service Across a Gateway ........   18
     2.2        - RFC 822 .......................................   19
     2.3        - X.400 .........................................   23
     3          - Basic Mappings ................................   34
     3.1        - Notation ......................................   34
     3.2        - ASCII and IA5 .................................   36
     3.3        - Standard Types ................................   36
     3.4        - Encoding ASCII in Printable String ............   40
     3.5        - RFC 1522 ......................................   41
     4          - Addressing and Message IDs ....................   43
     4.1        - A textual representation of MTS.ORAddress .....   44
     4.2        - Global Address Mapping ........................   52
     4.3        - EBNF.822-address <-> MTS.ORAddress ............   56
     4.4        - Repeated Mappings .............................   69
     4.5        - Directory Names ...............................   72
     4.6        - MTS Mappings ..................................   72
     4.7        - IPMS Mappings .................................   77



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     5          - Detailed Mappings .............................   83
     5.1        - RFC 822 -> X.400: Detailed Mappings ...........   83
     5.2        - Return of Contents ............................  100
     5.3        - X.400 -> RFC 822: Detailed Mappings ...........  100
     Appendix A - Mappings Specific to SMTP .....................  135
     1          - Probes ........................................  135
     2          - Long Lines ....................................  135
     3          - SMTP Extensions ...............................  135
     3.1        - SMTP Extension mapping to X.400 ...............  135
     3.2        - X.400 Mapping to SMTP Extensions ..............  136
          Appendix B - Mapping with X.400(1984) .................  138
     Appendix C - RFC 822 Extensions for X.400 access ...........  140
     Appendix D - Object Identifier Assignment ..................  141
     Appendix E - BNF Summary ...................................  142
     Appendix F - Text format for MCGAM distribution ............  152
     1          - Text Formats ..................................  152
     2          - Mechanisms to register and to distribute
     MCGAMs .....................................................  152
     3          - Syntax Definitions ............................  153
     4          - Table Lookups .................................  154
     5          - Domain -> OR Address MCGAM format .............  155
     6          - OR Address -> Domain MCGAM format .............  155
     7          - Domain -> OR Address of Preferred Gateway
     table ......................................................  156
     8          - OR Addresss -> domain of Preferred Gateway
     table ......................................................  156
     Appendix G - Conformance ...................................  157
     Appendix H - Change History: RFC 987, 1026, 1138, 1148
     ............................................................  159
     1          - Introduction ..................................  159
     2          - Service Elements ..............................  159
     3          - Basic Mappings ................................  160
     4          - Addressing ....................................  160
     5          - Detailed Mappings .............................  160
     6          - Appendices ....................................  161
     Appendix I - Change History: RFC 1148 to RFC 1327 ..........  162
     1          - General .......................................  162
     2          - Basic Mappings ................................  162
     3          - Addressing ....................................  162
     4          - Detailed Mappings .............................  163
     5          - Appendices ....................................  163
     Appendix J - Change History: RFC 1327 to this Document
     ............................................................  164
     1          - General .......................................  164



Kille                                                         [page 3]


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     2          - Service Elements ..............................  164
     3          - Basic Mappings ................................  164
     4          - Addressing ....................................  164
     5          - Detailed Mappings .............................  165
     6          - Appendices ....................................  165
          Appendix L - ASN.1 Summary ............................  167









































Kille                                                         [page 4]


     Chapter 1 -- Overview



     1.1.  X.400

     This document relates primarily to the ITU-T 1988 and 1992 X.400
     Series Recommendations / ISO IEC 10021 International Standard.
     This ISO/ITU-T standard is referred to in this document as
     "X.400", which is a convenient shorthand.  Any reference to the
     1984 Recommendations will be explicit.  Any mappings relating to
     elements which are in the 1992 version and not in the 1988
     version will be noted explicitly.  X.400 defines an Interpersonal
     Messaging System (IPMS), making use of a store and forward
     Message Transfer System.  This document relates to the IPMS, and
     not to wider application of X.400, such as EDI as defined in
     X.435.

     1.2.  RFC 822 and MIME

     RFC 822 evolved as a messaging standard on the DARPA (the US
     Defense Advanced Research Projects Agency) Internet.  RFC 822
     specifies an end to end message format, consisting of a header
     and an unstructured text body.   MIME (Multipurpose Internet Mail
     Extensions) specifies a structured message body format for use
     with RFC 822.  The term "RFC 822" is used in this document to
     refer to the combination of MIME and RFC 822. RFC 822 and MIME
     are used in conjunction with a number of different message
     transfer protocol environments.  The core of the MIXER
     specification is designed to work with any supporting message
     transfer protocol.

          One transfer protocol, SMTP, is of particular importance and
     is covered in MIXER.  On the Internet and other TCP/IP networks,
     RFC 822 is used in conjunction with
      RFC 821, also known as Simple Mail Transfer Protocol (SMTP)
     [30], in a manner conformant with the host requirements
     specification [10].  Use of MIXER with SMTP is defined in
     Appendix A.




Kille                                                         [page 6]


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     1.3.  The need for conversion

     There is a large community using RFC 822 based protocols for mail
     services, who will wish to communicate with users of the IPMS
     provided by X.400 systems.  This will also be a requirement in
     cases where communities intend to make a transition between the
     different technologies, as conversion will be needed to ensure a
     smooth service transition.  It is expected that there will be
     more than one gateway, and this specification will enable them to
     behave in a consistent manner.  Note that the term gateway is
     used to describe a component performing the mapping between RFC
     822 and X.400.  This is standard usage amongst mail implementors,
     but differs from that used by transport and network service
     implementors.

     Consistency between gateways is desirable to provide:

     1.   Consistent service to users.

     2.   The best service in cases where a message passes through
          multiple gateways.

     1.4.  General approach

     There are a number of basic principles underlying the details of
     the specification.  These principles are goals, and are not
     achieved in all aspects of the specification.

     1.   The specification should be pragmatic.  There should not be
          a requirement for complex mappings for "Academic" reasons.
          Complex mappings should not be required to support trivial
          additional functionality.

     2.   Subject to 1), functionality across a gateway should be as
          high as possible.

     3.   It is always a bad idea to lose information as a result of
          any transformation.  Hence, it is a bad idea for a gateway
          to discard information in the objects it processes.  This
          includes requested services which cannot be fully mapped.

     4.   Mail gateways  operate at a level above the layer on which
          they perform mappings.  This implies that the gateway shall
          not only be cognisant of the semantics of objects at the



Kille                                                         [page 7]


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          gateway level, but also be cognisant of higher level
          semantics.  If meaningful transformation of the objects that
          the gateway operates on is to occur, then the gateway needs
          to understand more than the objects themselves.

     5.   Subject to 1), the mapping should be reversible.  That is, a
          double transformation should bring you back to where you
          started.

     1.5.  Gatewaying Model

     1.5.1.  X.400

     X.400 defines the IPMS Abstract Service in X.420 , [11] which
     comprises of three basic services:

     1.   Origination

     2.   Reception

     3.   Management

     Management is a local interaction between the user and the IPMS,
     and is therefore not relevant to gatewaying.  The first two
     services consist of operations to originate and receive the
     following two objects:

     1.   IPM (Interpersonal Message). This has two components: a
          heading, and a body.  The body is structured as a sequence
          of body parts, which may be basic components (e.g., IA5
          text, or G3 fax), or forwarded Interpersonal Messages.  The
          heading consists of fields containing end to end user
          information, such as subject, primary recipients (To:), and
          importance.

     2.   IPN (Inter Personal Notification).  A notification  about
          receipt of a given IPM at the UA level.

     The Origination service also allows for origination of a probe,
     which is an object to test whether a given IPM could be correctly
     received.

     The Reception service also allows for receipt of Delivery Reports
     (DR), which indicate delivery success or failure.



Kille                                                         [page 8]


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          These IPMS Services utilise the Message Transfer System
     (MTS) Abstract Service [12].  The MTS Abstract Service provides
     the following three basic services:

     1.   Submission (used by IPMS Origination)

     2.   Delivery (used by IPMS Reception)

     3.   Administration (used by IPMS Management)

     Administration is a local issue, and so does not affect this
     standard.  Submission and delivery relate primarily to the MTS
     Message (comprising Envelope and Content), which carries an IPM
     or IPN (or other uninterpreted contents).  The Envelope includes
     a message identifier, an originator, and a list of recipients.
     Submission also includes the probe service, which supports the
     MTS Probe. Delivery also includes Reports, which indicate whether
     a given MTS Message has been delivered or not (or for a probe if
     delivery would have happened).

          The MTS is provided by MTAs which interact using the MTA
     (Message Transfer Agent) Service, which defines the interaction
     between MTAs, along with the procedures for distributed
     operation.  This service provides for transfer of MTS Messages,
     Probes, and Reports.

     1.5.2.  RFC 822

     RFC 822 is based on the assumption that there is an underlying
     service, which is here called the 822-MTS service.  The 822-MTS
     service provides three basic functions:

     1.   Identification of a list of recipients.

     2.   Identification of an error return address.

     3.   Transfer of an RFC 822 message.

     It is possible to achieve 2) within the RFC 822 header.

          This specification will be used most commonly with SMTP as
     the 822-MTS service.  The core MIXER specification is written so
     that it does not rely on non-basic 822-MTS services.   Use of
     non-basic SMTP services is described in Appendix A.  The core of



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     this document is written using SMTP terminology for 822-MTS
     services.

          An RFC 822 message consists of a header, and content which
     is uninterpreted ASCII text.  The header is divided into fields,
     which are the protocol elements.  Most of these fields are
     analogous to IPM heading fields, although some are analogous to
     MTS Service Elements or MTA Service Elements.

          RFC 822 supports delivery status notifications by use of the
     NOTARY mechanisms [28].

     1.5.3.  The Gateway

     Given this functional description of the two services, the
     functional nature of a gateway can now be considered.  It would
     be elegant to consider the SMTP (822-MTS) service mapping onto
     the MTS Service Elements and RFC 822 mapping onto an IPM, but
     there is a not a clear match between these services.  Another
     elegant approach would be to treat this document as the
     definition of an X.400 Access Unit (AU). In this case, the
     abstraction level is too high, and some necessary mapping
     function is lost.  It is necessary to consider that the IPM
     format definition, the IPMS Service Elements, the MTS Service
     Elements, and MTA Service Elements on one side are mapped into
     RFC 822 + SMTP on the other in a slightly tangled manner.  The
     details of the tangle will be made clear in Chapter 5.  Access to
     the MTA Service Elements is minimised.

          The following basic mappings are thus defined.  When going
     from RFC 822 to X.400, an RFC 822 message and the associated SMTP
     information is always mapped into an IPM (MTA, MTS, and IPMS
     Services) and a Delivery Status Notification is mapped onto a
     Report.  Going from X.400 to RFC 822, an RFC 822 message and the
     associated SMTP information may be derived from:

     1.   An IPN (MTA, MTS, and IPMS services)

     2.   An IPM (MTA, MTS, and IPMS services)

     A Report (MTA, and MTS Services) is mapped onto a delivery status
     notification.

     Probes (MTA Service) shall be processed by the gateway, as



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     discussed in Chapter 5.  MTS Messages containing Content Types
     other than those defined by the IPMS are not mapped by the
     gateway, and shall be rejected at the gateway if no other
     gatewaying procedure is defined.

          This specification is concerned with X.400 IPMS.  Future
     specifications may defined mappings for other X.400 content
     types.

     1.5.4.  Repeated Mappings

     The primary goal of this specification is to support single
     mappings, so that X.400 and RFC 822 users can communicate with
     maximum functionality.

          The mappings specified here are designed to work where a
     message traverses multiple times between X.400 and RFC 822. This
     is often essential, particularly in the case of distribution
     lists.  However, in general, this will lead to a level of service
     which is the lowest common denominator (approximately the
     services offered by RFC 822).

          Some RFC 822 networks may wish to use X.400 as an
     interconnection mechanism (typically for policy reasons), and
     this is fully supported.

          Where an X.400 message transfers to RFC 822 and then back to
     X.400, there is no expectation of X.400 services which do not
     have an equivalent service in standard RFC 822 being preserved -
     although this may be possible in some cases.

     1.6.  Support of X.400 (1984)

     The MIXER definition is based on the initial specification of RFC
     987 and in its addendum RFC 1026, which defined a mapping between
     X.400(1984) and RFC 822.  The core MIXER mapping is defined using
     the full 1988 version of X.400, and not to a 1984 compatible
     subset. New features of X.400(1988) can be used to provide a much
     cleaner mapping than that defined in RFC 987.  To interwork with
     1984 systems, Appendix B shall be followed.

          If a message is being transferred to an X.400(1984) system
     by way of X.400(1988) MTA it will give a slightly better service
     to follow the rules of Appendix B, than to downgrade without this



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     knowledge.   Downgrading specifications which supplement those
     specified in X.400 (X.419) are given in RFC 1328[22] and RFC 1496
     (HARPOON) [5].

     1.7.  X.400 (1992)

     X.400 (1992) features are not used by the core of this mapping,
     and so there is not an equivalent downgrade problem.

     1.8.  MIME

     MIME format messages are generated by this mapping.   As MIME
     messages are fully RFC 822 compliant, this will not cause
     problems with systems which are not MIME capable.

     1.9.  Body Parts

     MIME and X.400 IPMS can both carry arbitrary body parts. MIME
     defines a mechanism for adding new body parts, and new body parts
     are registered with the IANA. X.400 defines a mechanism adding
     new body parts, usually referred to as Body Part 15.  Extensions
     are defined by Object Identifiers, so there is no requirement for
     a central body part registration authority.   The Electronic
     Messaging Association (EMA) maintains a list of some commonly
     used body parts.   The EMA has specified a mechanism to use the
     File Transfer Body Part (FTBP) as a more generic means to support
     message attachments.  This approach is gaining widespread
     commercial support.

          The mapping between X.400 and MIME body parts is defined in
     the companion MIXER specification, referenced here as RFC 1494bis
     [8].  This document is an update of RFC 1494 [6].

     Editor's Note:
          References to 1494bis will be resolved as these two
          documents are expected to progress in parallel.

     These two specifications together form the complete MIXER









Kille                                                        [page 12]


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     Mapping.

     1.10.  Local and Global Scenarios

     There are two basic scenarios for X.400/MIME interworking:

     Global Scenario
          There are two global mail networks (Internet/MIME and
          X.400), interconnected by multiple gateways.   Objects may
          be transferred over multiple gateways, and so it is
          important that gateways behave in a coherent fashion.
          MIXER is critical to support this scenario.

     Local Scenario
          A gateway is used to connect a closed community to a global
          mail network (this could be enforced by connectivity or
          gateway authorisation policy).  This is a common commercial
          scenario.  MIXER is useful to support this scenario, as it
          allows an industry standard provision of service, but this
          could be supported by something which was MIXER-like.

     A solution for the global scenario will work for the local
     scenario.  However, there are aspects of MIXER which have
     significant implementation or deployment effort (the global
     mapping is the major one, but there are other details too) which
     and are needed to support the global scenario, but are not needed
     in the local scenario.

          Note that the local scenario may be the driving force for
     most deployments, and support of the global scenario may be an
     important secondary goal.

          There is also a transition effect.  Gateways which are
     initially deployed in a strict local scenario  situation start to
     find themselves in a global scenario.  A common case is ADMD
     provided gateways, which are targeted strictly at the local
     scenario.  In practice they soon start to operate in the global
     scenario, because of distribution lists and messages exchanged
     with X.400 users that are not customers of the ADMD.  At this
     point, users are hurt by the restrictions of a local scenario
     gateway.

          Note that conformance to MIXER applies to an instantiation
     of a gateway, not just an implementation (although clearly it is



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     critical that the implementation is capable of being operated in
     a conformant manner).

          MIXER's conformance target is the global scenario, and the
     specification of MIXER defines operation in this way.

     1.11.  Compatibility with previous versions

     The changes between this and older versions of the document are
     given in Appendices H, I and J.    These are RFCs 987, 1026,
     1138, 1148 and 1327.  This document is a revision of RFC 1327
     [21].  As far as possible, changes have been made in a compatible
     fashion.

     1.12.  Aspects not covered

     There have been a number of cases where previous versions of this
     document were used in a manner which was not intended.  This
     section is to make clear some limitations of scope.  In
     particular, this specification does not specify:

     -    Extensions of RFC 822 to provide access to all X.400
          services

     -    X.400 user interface definition

     These are really coupled.  To map the X.400 services, this
     specification defines a number of extensions to RFC 822.  As a
     side effect, these give the 822 user access to SOME X.400
     services.  However, the aim on the RFC 822 side is to preserve
     current service, and it is intentional that access is not given
     to all X.400 services.  Thus, it will be a poor choice for X.400
     implementors to use MIXER  as an interface - there are too many
     aspects of X.400 which cannot be accessed through it.  If a text
     interface is desired, a specification targeted at X.400, without
     RFC 822 restrictions, would be more appropriate.  Some optional
     and limited extensions in this area have proved useful, and are
     defined in Appendix C.

     1.13.  Subsetting

     This proposal specifies a mapping which is appropriate to
     preserve services in existing RFC 822 communities.
     Implementations and specifications which subset this



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     specification are non-conformant and strongly discouraged.

     1.14.  Specification Language

     ISO and Internet standards have clear definitions as to the style
     of language used.   This specification maps between  ISO/ITU-T
     protocol and Internet protocols.  This document uses ISO
     terminology for the following reasons:

     1.   This was done in previous versions.

     2.   ISO language may be mechanically converted to Internet
          language, but not vice versa.

     The key elements of the ISO rules are:

     1.   All mandatory features shall clearly be indicated by
          imperative statements or the word "shall" or "shall not".

     2.   Optional features shall be indicated by the word "may".

     3.   The word "should" and the phrase "may not" shall not be
          used.

     In some cases the specification issues guidance on use of
     optional features, by use of the the phrase word "recommended" or
     "not recommended".

     To interpet this document according to Internet rules, replace
     every occurrence of "shall" with "must".

     1.15.  Related Specifications

     Mappings between Mail-11 and X.400 and Mail-11 and rfc822 are
     described in RFC1405, using mappings related to those defined
     here [2].

     1.16.  Document Structure

     This document has five chapters:

     1.   Overview - this chapter.

     2.   Service Elements - This describes the (end user) services



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          mapped by a gateway.

     3.   Basic mappings - This describes some basic notation used in
          Chapters 3-5, the mappings between character sets, and some
          fundamental protocol elements.

     4.   Addressing - This considers the mapping between X.400 OR
          names and RFC 822 addresses, which is a fundamental gateway
          component.

     5.   Detailed Mappings - This describes the details of all other
          mappings.

     There are also ten appendices.



     WARNING:
          THE REMAINDER OF THIS SPECIFICATION IS TECHNICALLY DETAILED.
          IT WILL NOT MAKE SENSE, EXCEPT IN THE CONTEXT OF RFC 822 AND
          X.400 (1988).  DO NOT ATTEMPT TO READ THIS DOCUMENT UNLESS
          YOU ARE FAMILIAR WITH THESE SPECIFICATIONS.

     1.17.  Acknowledgements

     The work in this specification was substantially based on RFC 987
     and RFC 1148, which had input from many people, who are credited
     in the respective documents.

          A number of comments from people on RFC 1148 lead to RFC
     1327.  In particular, there were comments and suggestions from:
     Maurice Abraham (HP); Harald Alvestrand (Sintef); Peter Cowen
     (X-Tel); Jim Craigie (JNT); Ella Gardner (MITRE); Christian
     Huitema (Inria); Erik Huizer (SURFnet); Neil Jones (DEC); Ignacio
     Martinez (IRIS); Julian Onions (X-Tel); Simon Poole (SWITCH);
     Clive Roberts (Data General); Pete Vanderbilt (SUN); Alan Young
     (Concurrent).

          RFC 1327 has been widely adopted, and a review team was
     formed.   This comprised of:  Urs Eppenberger (SWITCH)(Chair);
     Claudio Allocchio (INFN); Harald Alvestrand (UNINETT); Dave
     Crocker (Brandenburg); Ned Freed (Innosoft); Erik Huizer
     (SURFnet); Steve Kille (Isode); Peter Sylvester (GC Tech)




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          Harald Alvestrand also supplied the tables mapping DSN
     status codes with X.400 codes.  Ned Freed defined parts of the
     File Transfer Body Part mapping.

          Comment and input has also been received from:  Bengt
     Ackzell (Generic Systems); Samir Albadine (Transpac); Mark Boyes
     (DEC); Larry Campbell (Boston Software Works); Jacqui Caren
     (Cray); Allan Cargille (MCI); Kevin Carrosso (Innosoft); Charlie
     Combs (OIW); Jim Craigie (Net-Tel); Eamon Doyle (Isocor); Efifion
     Edem (SITA); Jyrki Heikkinen (ICL); Edward Hibbert (DCL); Jeroun
     Houttin (Terena); Kevin Jordan (CDS); Paul Kingsnorth (DEC);
     Carl-Uno Manros (Manros Consulting); Suzan Mendes (Telis); Robert
     Miles (Softswitch); Roger Mizumorri (Enterprise Solutions Ltd);
     Keith Moore (University of Tennessee); Ruth Moulton (Net-Tel)
     Michel Musy (Bull); Kenji Nonaka (NTT):  The OIW MHSIG; Tom
     Oliphant (SWITCH); Julian Onions (NEXOR); Jacob Palme (KTH);
     Olivier Paridaens (ULB); Mary la Roche (Citicorp); John Setsaas
     (Maxware); Russell Sharpe (DCL); Patrick Soulier (CCETT);
     Eftimios Tsigros (Universite Libre de Bruxelles); Sean Turner
     (IECA); Mark Wahl (Isode); David Wilson (Isode); Bill Wohler
     (Worldtalk); Alan Young (Isode); Alain Zahm (Telis).


























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     Chapter 2 - Service Elements


     This chapter considers the services offered across a gateway
     built according to this specification.  It gives a view of the
     functionality provided by such a gateway for communication with
     users in the opposite domain.  This chapter considers service
     mappings in the context of SINGLE transfers only, and not
     repeated mappings through multiple gateways.


     2.1.  The Notion of Service Across a Gateway

     RFC 822 and X.400 provide a number of services to the end user.
     This chapter describes the extent to which each service can be
     supported across an X.400 <-> RFC 822 gateway.  The cases
     considered are single transfers across such a gateway, although
     the problems of multiple crossings are noted where appropriate.

     2.1.1.  Origination of Messages

     When a user originates a message, a number of services are
     available.  Some of these imply actions (e.g., delivery to a
     recipient), and some are insertion of known data (e.g.,
     specification of a subject field).  This chapter describes, for
     each offered service, to what extent it is supported for a
     recipient accessed through a gateway.  There are three levels of
     support:

     Supported
          The corresponding protocol elements map well, and so the
          service can be fully provided.

     Not Supported
          The service cannot be provided, as there is a complete
          mismatch.

     Partial Support
          The service can be partially fulfilled.

     In the first two cases, the service is simply marked as
     "Supported" or "Not Supported".  Some explanation may be given if
     there are additional implications, or the (non) support is not
     intuitive.  For partial support, the level of partial support is



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     summarised.  Where partial support is good,  this will be
     described by a phrase such as "Supported by use of.....".  A
     common case of this is where the service is mapped onto a non-
     standard service on the other side of the gateway, and this would
     have lead to support if it had been a standard service.  In many
     cases, this is equivalent to support.  For partial support, an
     indication of the mechanism is given, in order to give a feel for
     the level of support provided.  Note that this is not a
     replacement for Chapter 5, where the mapping is fully specified.

          If a service is described as supported, this implies:

     -    Semantic correspondence.

     -    No (significant) loss of information.

     -    Any actions required by the service element.

     An example of a service gaining full support: If an RFC 822
     originator specifies a Subject:  field, this is considered to be
     supported, as an X.400 recipient will get a subject indication.

     In many cases, the required action will simply be to make the
     information available to the end user.  In other cases, actions
     may imply generating a delivery report.

          All RFC 822 services are supported or partially supported
     for origination.  The implications of non-supported X.400
     services is described under X.400.


     2.1.2.  Reception of Messages

     For reception, the list of service elements required to support
     this mapping is specified.  This is really an indication of what
     a recipient might expect to see in a message which has been
     remotely originated.

     2.2.  RFC 822

     RFC 822 does not explicitly define service elements, as distinct
     from protocol elements.  However, all of the RFC 822 header
     fields, with the exception of trace, can be regarded as
     corresponding to implicit RFC 822 service elements.



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     2.2.1.  Origination in RFC 822

     A mechanism of mapping, used in several cases, is to map the RFC
     822 header into a heading extension in the IPM (InterPersonal
     Message).  This can be regarded as partial support, as it makes
     the information available to any X.400 implementations which are
     interested in these services. Communities which require
     significant RFC 822 interworking are recommended to require that
     their X.400 User Agents are able to display these heading
     extensions.  Support for the various service elements (headers)
     is now listed.

     Date:
          Supported.

     From:
          Supported.  For messages where there is also a sender field,
          the mapping is to "Authorising Users Indication", which has
          subtly different semantics to the general RFC 822 usage of
          From:.

     Sender:
          Supported.

     Reply-To:
          Supported.

     To:  Supported.

     Cc:  Supported.

     Bcc: Supported.

     Message-Id:
          Supported.

     In-Reply-To:
          Supported, for a single reference.  Where multiple
          references are given, partial support is given by mapping to
          "Cross Referencing Indication".  This gives similar
          semantics.

     References:
          Supported.



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     Keywords:
          Supported by use of a heading extension.

     Subject:
          Supported.

     Comments:
          Supported by use of a heading extension.

     Encrypted:
          Supported by use of a heading extension.

     Content-Language:
          Supported.

     Resent-*
          Supported by use of a heading extension.  Note that
          addresses in these fields are mapped onto text, and so are
          not accessible to the X.400 user as addresses.  In
          principle, fuller support would be possible by mapping onto
          a forwarded IP Message, but this is not suggested.

     Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g., "Fruit-of-the-day:") are supported by use of
          heading extensions.

     MIME introduces a number of headings.  Support is defined in RFC
     1494bis.

     2.2.2.  Reception by RFC 822

     This considers reception by an RFC 822 User Agent of a message
     originated in an X.400 system and transferred across a gateway.
     The following standard services (headers) may be present in such
     a message:

     Date:

     From:

     Sender:

     Reply-To:



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     To:

     Cc:

     Bcc:

     Message-Id:

     In-Reply-To:

     References:

     Subject:

     Content-Type: (See RFC 1494bis)

     Content-Transfer-Encoding: (See RFC 1494bis)

     MIME-Version: (See RFC 1494bis)

     The following services (headers) may be present in the header of
     a message. These are defined in more detail in Chapter 5 (5.3.4,
     5.3.6, 5.3.7):

     Autoforwarded:

     Autosubmitted:

     X400-Content-Identifier:

     Content-Language:

     Conversion:

     Conversion-With-Loss:

     Delivery-Date:

     Discarded-X400-IPMS-Extensions:

     Discarded-X400-MTS-Extensions:

     DL-Expansion-History:




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     Deferred-Delivery:

     Expires:

     Importance:

     Incomplete-Copy:

     Latest-Delivery-Time:

     Message-Type:

     Original-Encoded-Information-Types:

     Originator-Return-Address:

     Priority:

     Reply-By:

     Sensitivity:

     Supersedes:

     X400-Content-Type:

     X400-MTS-Identifier:

     X400-Originator:

     X400-Received:

     X400-Recipients:

     2.3.  X.400

     2.3.1.  Origination in X.400

     When mapping services from X.400 to RFC 822 which are not
     supported by RFC 822, new RFC 822 headers are defined, and
     registered by publication in this standard. It is intended that
     co-operating RFC 822 systems may also use them.  Where these new
     fields are used, and no system action is implied, the service can
     be regarded as being partially supported.  Chapter 5 describes



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     how to map X.400 services onto these new headers.  Other elements
     are provided, in part, by the gateway as they cannot be provided
     by RFC 822.

          Some service elements are marked N/A (not applicable).
     There are five cases, which are marked with different comments:

     N/A (local)
          These elements are only applicable to User Agent / Message
          Transfer Agent interaction and so they cannot apply to RFC
          822 recipients.

     N/A (PDAU)
          These service elements are only applicable where the
          recipient is reached by use of a Physical Delivery Access
          Unit (PDAU), and so do not need to be mapped by the gateway.

     N/A (reception)
          These services  are only applicable for reception.

     N/A (prior)
          If requested, this service shall be performed prior to the
          gateway.

     N/A (MS)
          These services are only applicable to Message Store (i.e., a
          local service).

          Finally, some service elements are not supported.  In
     particular, the new security services are not mapped onto RFC
     822.  Unless otherwise indicated, the behaviour of service
     elements marked as not supported will depend on the criticality
     marking supplied by the user.  If the element is marked as
     critical for transfer or delivery, a non-delivery notification
     will be generated.  Otherwise, the service request will be
     ignored.

     2.3.1.1.  Basic Interpersonal Messaging Service

     These are the mandatory IPM services as listed in Section 19.8 of
     X.400 / ISO/IEC 10021-1, listed here in the order given. Section
     19.8 has cross references to short definitions of each service.

     Access management



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          N/A (local).

     Content Type Indication
          Supported by a new RFC 822 header (X400-Content-Type:).

     Converted Indication
          Supported by a new RFC 822 header (X400-Received:).

     Delivery Time Stamp Indication
          N/A (reception).

     IP Message Identification
          Supported.

     Message Identification
          Supported, by use of a new RFC 822 header
          (X400-MTS-Identifier).  This new header is required, as
          X.400 has two message-ids whereas RFC 822 has only one (see
          IP Message Identification

     Non-delivery Notification
          Not supported in all cases.  Supported where the recipient
          system supports NOTARY DSNs.  In general all RFC 822 systems
          will return error reports by use of IP messages.  In other
          service elements, this pragmatic result can be treated as
          effective support of this service element.

     Original Encoded Information Types Indication
          Supported as a new RFC 822 header
          (Original-Encoded-Information-Types:).

     Submission Time Stamp Indication
          Supported.

     Typed Body
          Support is defined in RFC 1494bis.

     User Capabilities Registration
          N/A (local).

     2.3.1.2.  IPM Service Optional User Facilities

     This section describes support for the optional (user selectable)
     IPM services as listed in Section 19.9 of X.400 / ISO/IEC 10021-



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     1, listed here in the order given.  Section 19.9 has cross
     references to short definitions of each service.

     Additional Physical Rendition
          N/A (PDAU).

     Alternate Recipient Allowed
          Not supported.  There is no RFC 822 service equivalent to
          prohibition of alternate recipient assignment (e.g., an RFC
          822 system may freely send an undeliverable message to a
          local postmaster).  A MIXER gateway has two conformant
          options.  The first is not to gateway a message requesting
          prohibition of alternate recipient, as this control cannot
          be guaranteed.  This option supports the service, but may
          cause unacceptable level of message rejections. The second
          is to gateway the message on the basis that there is no
          alternate recipient service in RFC 822. RFC 1327 allowed
          only the second option.   If the first option is shown to be
          operationally effective, it may be the only option in future
          versions of MIXER.

     Authorising User's Indication
          Supported.

     Auto-forwarded Indication
          Supported as new RFC 822 header (Auto-Forwarded:).

     Basic Physical Rendition
          N/A (PDAU).

     Blind Copy Recipient Indication
          Supported.

     Body Part Encryption Indication
          Supported by use of a new RFC 822 header
          (Original-Encoded-Information-Types:), although in most
          cases it will not be possible to map the body part in
          question.

     Content Confidentiality
          Not supported.

     Content Integrity
          Not supported.



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     Conversion Prohibition
          Supported. Operation defined in RFC 1494bis.

     Conversion Prohibition in Case of Loss of Information
          Supported.  Operation defined in RFC 1494bis.

     Counter Collection
          N/A (PDAU).

     Counter Collection with Advice
          N/A (PDAU).

     Cross Referencing Indication
          Supported.

     Deferred Delivery
          N/A (prior).  This service shall always be provided by the
          MTS prior to the gateway.  A new RFC 822 header
          (Deferred-Delivery:) is provided to transfer information on
          this service to the recipient.

     Deferred Delivery Cancellation
          N/A (local).

     Delivery Notification
          Supported.  This is performed at the gateway, but may be
          performed at the end system if the end system supports
          NOTARY.  Thus, a notification is sent by the gateway to the
          originator.

     Delivery via Bureaufax Service
          N/A (PDAU).

     Designation of Recipient by Directory Name
          N/A (local).

     Disclosure of Other Recipients
          Supported by use of a new RFC 822 header (X400-Recipients:).
          This is descriptive information for the RFC 822 recipient,
          and is not reverse mappable.

     DL Expansion History Indication
          Supported by use of a new RFC 822 header
          (DL-Expansion-History:).



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     DL Expansion Prohibited
          Distribution List means MTS supported distribution list, in
          the manner of X.400.  This service does not exist in the RFC
          822 world, although RFC 822 supports distribution list
          functionality.  There is no SMTP leve control to prohibit
          distribution list expansion.   A MIXER gateway has two
          conformant options.  The first is not to gateway a message
          requesting DL expansion prohibition, as this control cannot
          be guaranteed.  This option supports the service, but may
          cause unacceptable level of message rejections. The second
          is to gateway the message on the basis that there is no
          distribution list service in RFC 822. RFC 1327 allowed only
          the second option.   If the first option is shown to be
          operationally effective, it may be the only option in future
          versions of MIXER.

     Express Mail Service
          N/A (PDAU).

     Expiry Date Indication
          Supported as new RFC 822 header (Expires:).  In general, no
          automatic action can be expected.

     Explicit Conversion
          N/A (prior).

     Forwarded IP Message Indication
          Supported.

     Grade of Delivery Selection
          Not Supported.  There is no equivalent service in RFC 822.

     Importance Indication
          Supported as new RFC 822 header (Importance:).

     Incomplete Copy Indication
          Supported as new RFC 822 header (Incomplete-Copy:).

     Language Indication
          Supported as new RFC 822 header (Content-Language:).

     Latest Delivery Designation
          Not supported.  A new RFC 822 header (Latest-Delivery-Time:)
          is provided, which may be used by the recipient for general



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          information, but will not be acted on by the SMTP
          infrastrucuture.

     Message Flow Confidentiality
          Not supported.

     Message Origin Authentication
          N/A (reception).

     Message Security Labelling
          Not supported.

     Message Sequence Integrity
          Not supported.

     Multi-Destination Delivery
          Supported.

     Multi-part Body
          Supported.

     Non Receipt Notification Request
          Not supported.

     Non Repudiation of Delivery
          Not supported.

     Non Repudiation of Origin
          N/A (reception).

     Non Repudiation of Submission
          N/A (local).

     Obsoleting Indication
          Supported as new RFC 822 header (Supersedes:).

     Ordinary Mail
          N/A (PDAU).

     Originator Indication
          Supported.

     Originator Requested Alternate Recipient
          Not supported, but is placed as comment next to address



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          (X400-Recipients:).

     Physical Delivery Notification by MHS
          N/A (PDAU).

     Physical Delivery Notification by PDS
          N/A (PDAU).

     Physical Forwarding Allowed
          Supported by use of a comment in a new RFC 822 header
          (X400-Recipients:), associated with the recipient in
          question.

     Physical Forwarding Prohibited
          Supported by use of a comment in a new RFC 822 header
          (X400-Recipients:), associated with the recipient in
          question.

     Prevention of Non-delivery notification
          Supported where SMTP and NOTARY are available.  In other
          cases formally supported, as delivery notifications cannot
          be generated by RFC 822.  In practice, errors will be
          returned as IP Messages, and so this service may appear not
          to be supported (see Non-delivery Notification).

     Primary and Copy Recipients Indication
          Supported

     Probe
          Supported at the gateway (i.e., the gateway services the
          probe).

     Probe Origin Authentication
          N/A (reception).

     Proof of Delivery
          Not supported.

     Proof of Submission
          N/A (local).

     Receipt Notification Request Indication
          Not supported.




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     Redirection Disallowed by Originator
          Redirection means MTS supported redirection, in the manner
          of X.400.  This service does not exist in the RFC 822 world.
          RFC 822 redirection (e.g., aliasing) is regarded as an
          informal redirection mechanism, beyond the scope of this
          control.  Messages will be sent to RFC 822, irrespective of
          whether this service is requested. In practice, control of
          this service is not supported.

     Registered Mail
          N/A (PDAU).

     Registered Mail to Addressee in Person
          N/A (PDAU).

     Reply Request Indication
          Supported as comment next to address.

     Replying IP Message Indication
          Supported.

     Report Origin Authentication
          N/A (reception).

     Request for Forwarding Address
          N/A (PDAU).

     Requested Delivery Method
          N/A (local).   The service request is dealt with at
          submission time.  Any such request is made available through
          the gateway by use of a comment associated with the
          recipient in question.

     Return of Content
          Supported where SMTP and NOTARY are used. In principle for
          other situations, this is N/A, as non-delivery notifications
          are not supported.  In practice, most RFC 822 systems will
          return part or all of the content along with the IP Message
          indicating an error (see Non-delivery Notification).

     Sensitivity Indication
          Supported as new RFC 822 header (Sensitivity:).

     Special Delivery



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          N/A (PDAU).

     Stored Message Deletion
          N/A (MS).

     Stored Message Fetching
          N/A (MS).

     Stored Message Listing
          N/A (MS).

     Stored Message Summary
          N/A (MS).

     Subject Indication
          Supported.

     Undeliverable Mail with Return of Physical Message
          N/A (PDAU).

     Use of Distribution List
          In principle this applies only to X.400 supported
          distribution lists (see DL Expansion Prohibited).
          Theoretically, this service is N/A (prior).  In practice,
          because of informal RFC 822 lists, this service can be
          regarded as supported.

     Auto-Submitted Indication
          Supported

     2.3.2.  Reception by X.400

     2.3.2.1.  Standard Mandatory Services

     The following standard IPM mandatory  user facilities are
     required for reception of RFC 822 originated mail by an X.400 UA.


     Content Type Indication

     Delivery Time Stamp Indication

     IP Message Identification




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     Message Identification

     Non-delivery Notification

     Original Encoded Information Types Indication

     Submission Time Stamp Indication

     Typed Body

     2.3.2.2.  Standard Optional Services

     The following standard IPM optional user facilities are required
     for reception of RFC 822 originated mail by an X.400 UA.

     Authorising User's Indication

     Blind Copy Recipient Indication

     Cross Referencing Indication

     Originator Indication

     Primary and Copy Recipients Indication

     Replying IP Message Indication

     Subject Indication

     2.3.2.3.  New Services

     A new X.400 service "RFC 822 Header Field" is defined using the
     extension facilities.  This allows for any RFC 822 header field
     to be represented.  It may be present in RFC 822 originated
     messages which are received by an X.400 UA.












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     Chapter 3 Basic Mappings



     3.1.  Notation

     The X.400 protocols are encoded in a structured manner according
     to ASN.1, whereas RFC 822 is text encoded.  To define a detailed
     mapping, it is necessary to refer to detailed protocol elements
     in each format.  A notation to achieve this is described in this
     section.


     3.1.1.  RFC 822

     Structured text is defined according to the Extended Backus Naur
     Form (EBNF) defined in Section 2 of RFC 822 [16].  In the EBNF
     definitions used in this specification, the syntax rules given in
     Appendix D of RFC 822 are assumed.  When these EBNF tokens are
     referred to outside an EBNF definition, they are identified by
     the string "822." appended to the beginning of the string (e.g.,
     822.addr-spec).  Additional syntax rules, to be used throughout
     this specification, are defined in this chapter.

     The EBNF is used in two ways.

     1.   To describe components of RFC 822 messages (or of SMTP
          components).  When these new EBNF tokens are referred to
          outside an EBNF definition, they are identified by the
          string "EBNF." appended to the beginning of the string
          (e.g., EBNF.importance).

     2.   To describe the structure of IA5 or ASCII information not in
          an RFC 822 message.

     For all new EBNF, tokens will either be self delimiting, or be
     delimited by self delimiting tokens.  Comments and LWSP are not
     used as delimiters, except for the following cases, where LWSP
     may be inserted according to RFC 822 rules.

     -    Around the ":" in all headers

     -    EBNF.labelled-integer




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     -    EBNF.object-identifier

     -    EBNF.encoded-info

     RFC 822 folding rules are applied to all headers.  Comments are
     never used in these new headers.

          This notation is used in a modified form to refer to NOTARY
     EBNF [28].  For this EBNF, the keyword EBNF it replaces with DSN,
     for example DSN.final-recipient-field fields.

     3.1.2.  ASN.1

     An element is referred to with the following syntax, defined in
     EBNF:

             element         = service "." definition *( "." definition )
             service         = "IPMS" / "MTS" / "MTA"
             definition      = identifier / context
             identifier      = ALPHA *< ALPHA or DIGIT or "-" >
             context         = "[" 1*DIGIT "]"

     The EBNF.service keys are shorthand for the following service
     specifications:

     IPMS IPMSInformationObjects defined in Annex E of X.420 / ISO
          10021-7.

     MTS  MTSAbstractService defined in Section 9 of X.411 / ISO
          10021-4.

     MTA  MTAAbstractService defined in Section 13 of X.411 / ISO
          10021-4.

     FTBP File Transfer Body Part, as defined in [27].

     The first EBNF.identifier identifies a type or value key in the
     context of the defined service specification.   Subsequent
     EBNF.identifiers identify a value label or type in the context of
     the first identifier (SET or SEQUENCE).  EBNF.context indicates a
     context tag, and is used where there is no label or type to
     uniquely identify a component.  The special EBNF.identifier
     keyword "value" is used to denote an element of a sequence.




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     For example, IPMS.Heading.subject defines the subject element of
     the IPMS heading.  The same syntax is also used to refer to
     element values.  For example,
     MTS.EncodedInformationTypes.[0].g3Fax refers to a value of
     MTS.EncodedInformationTypes.[0] .

     3.2.  ASCII and IA5

     A gateway will interpret all IA5 as ASCII.  Thus, mapping between
     these forms is conceptual.

     3.3.  Standard Types

     There is a need to convert between ASCII text and some of the
     types defined in ASN.1 [14].  For each case, an EBNF syntax
     definition is given, for use in all of this specification, which
     leads to a mapping between ASN.1, and an EBNF construct.  All
     EBNF syntax definitions of ASN.1 types are in lower case, whereas
     ASN.1 types are referred to with the first letter in upper case.
     Except as noted, all mappings are symmetrical.

     3.3.1.  Boolean

     Boolean is encoded as:

             boolean = "TRUE" / "FALSE"


     3.3.2.  NumericString

     NumericString is encoded as:

             numericstring = *(DIGIT / " ")


     3.3.3.  PrintableString

     PrintableString is a restricted IA5String defined as:

             printablestring  = *( ps-char )
             ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                                / "," / "-" / "." / "/" / ":" / "=" / "?"
             ps-delim         = "(" / ")"
             ps-char          = ps-delim / ps-restricted-char



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     This can be used to represent real printable strings in EBNF.

     3.3.4.  T.61String

     In cases where T.61 strings are only used for conveying human
     interpreted information, the aim of a mapping is  to render the
     characters appropriately in the remote character set, rather than
     to maximise reversibility.  For these cases, there are two
     options, both of which are conformant to this specification:

     1.   The mappings to IA5 defined in ITU-T Recommendation X.408
          (1988) may be used [13].  These will then be encoded in
          ASCII.   This is the approach mandated in RFC 1327.

     2.   This mapping may be used if the characters are not contained
          within ASCII repertoire, but are all in an IANA-registered
          character set.  Use the encoding defined in RFC 1522 [9] to
          generate appropriate encoded-words.  If this mapping is
          used, the character set ISO-8859-1 shall be used if all of
          the characters needed are available in this repertoire.  In
          other cases, the character set TELETEX shall be used.  The
          details of this character set is defined in the Appendix C
          of RFC1494bis.

          There is also a need to represent Teletex Strings in ASCII,
     for some aspects of OR Address.  For these, the following
     encoding is used:

             teletex-string   = *( ps-char / t61-encoded )
             t61-encoded      = "{" 1* t61-encoded-char "}"
             t61-encoded-char = 3DIGIT

     Characters in EBNF.ps-char are mapped simply.  Other octets,
     including control characters,  are mapped using a quoting
     mechanism similar to the printable string mechanism.  Each octet
     is represented as 3 decimal digits.   For example, the Yen
     character (hex A5) is represented as {165}.   As the three
     character string, a, yen character, b, would be represented as
     either "a{165}b".

          The use of escape sequences follows that set down for ASN1.
     in ISO 8825-1, with the additional specifiction that the default
     G1 page is ISO Latin 1.   The page settings may be changed by
     escape sequences.  Changes of the settings hold within a pair of



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     curly brackets ({}), and the settings revert to the default after
     the right bracket (}) (i.e., they do not carry forward to
     subsequent T.61 encoding).

     There are a number of places where a string may have a Teletex
     and/or Printable String representation.  The following EBNF is
     used to represent this.

             teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]

     The natural mapping is restricted to EBNF.ps-char, in order to
     make the full BNF easier to parse.  An example is:

                     "yen*{165}"


     3.3.5.  UTCTime

     Both UTCTime and the RFC 822 822.date-time syntax contain:  Year,
     Month, Day of Month, hour, minute, second (optional), and
     Timezone (technically a time differential in UTCTime).
     822.date-time also contains an optional day of the week, but this
     is redundant.  With the exception of Year, a symmetrical mapping
     can be made between these constructs.

     Note:
          In practice, a gateway will need to parse various illegal
          variants on 822.date-time.  In cases where 822.date-time
          cannot be parsed, it is recommended that the derived UTCTime
          is set to the value at the time of translation.  Such errors
          may be noted in an RFC 822 comment, to aid detection and
          correction.

     When mapping to X.400, the UTCTime format which specifies the
     timezone offset shall be used.

     When mapping to RFC 822, the 822.date-time format shall include a
     numeric timezone offset (e.g., -0500).

     When mapping time values, the timezone shall be preserved as
     specified.  The date shall not be normalised to any other
     timezone.

     RFC 822, as modified by RFC 1123, requires use of a four digit



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     year.  Note that the original RFC 822 uses a two digit date,
     which is no longer legal.  UTCTime uses a two digit date.  To map
     a year from RFC 822 to X.400, simply use the last two digits.
     To map a year from X.400 to RFC 822, assume that the two digit
     year refers to a year in the 10 year epoch 1980-2079.

     3.3.6.  Integer

     A basic ASN.1 Integer will be mapped onto EBNF.numericstring.  In
     many cases ASN.1 will enumerate Integer values or use ENUMERATED.
     An EBNF encoding labelled-integer is provided. When mapping from
     EBNF to ASN.1, only the integer value is mapped, and the
     associated text is discarded.  When mapping from ASN.1 to EBNF, a
     text label may be added.  It is recommended that this is done
     wherever possible and that clear text labels are chosen.

          A second encoding labelled-integer-2 is provided. This is
     used in DSNs, where the parsing rules will treat the text as a
     comment. This definition was not present in RFC 1327.

             labelled-integer ::= [ key-string ] "(" numericstring ")"

             labelled-integer-2 ::= [ numericstring ] "(" key-string ")"

             key-string      = *key-char
             key-char        = <a-z, A-Z, 0-9, and "-">


     3.3.7.  Object Identifier

     Object identifiers are represented in a form similar to that
     given in ASN.1.  The order is the same as for ASN.1 (big-endian).
     The numbers are mandatory, and used when mapping from the ASCII
     to ASN.1.  The key-strings are optional.  It is recommended that
     as many strings as possible are generated when mapping from ASN.1
     to ASCII, to facilitate user recognition.

             object-identifier  ::= oid-comp object-identifier
                             | oid-comp

             oid-comp ::= [ key-string ] "(" numericstring ")"

     An example representation of an object identifier is:




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             joint-iso-ccitt(2) mhs (6) ipms (1) ep (11) ia5-text (0)

             or

             (2) (6) (1)(11)(0)

     Because of the use of brackets and the conflict with the RFC 822
     comment convention, MIXER is defines so that the EBNFobject-
     identifier definition is not used in structured fields.

     3.4.  Encoding ASCII in Printable String

     Some information in RFC 822 is represented in ASCII, and needs to
     be mapped into X.400 elements encoded as printable string.  For
     this reason, a mechanism to represent ASCII encoded as
     PrintableString is needed.

          A structured subset of EBNF.printablestring is now defined.
     This shall be used to encode ASCII in the PrintableString
     character set.

             ps-encoded       = *( ps-restricted-char / ps-encoded-char )
             ps-encoded-char  = "(a)"               ; (@)
                              / "(p)"               ; (%)
                              / "(b)"               ; (!)
                              / "(q)"               ; (")
                              / "(u)"               ; (_)
                              / "(l)"               ; "("
                              / "(r)"               ; ")"
                              / "(" 3DIGIT ")"

     The 822.3DIGIT in EBNF.ps-encoded-char shall have range 0-127,
     and is interpreted in decimal as the corresponding ASCII
     character.  Special encodings are given for: at sign (@), percent
     (%), exclamation mark/bang (!), double quote ("), underscore (_),
     left bracket ((), and right bracket ()).  These characters, with
     the exception of round brackets, are not included in
     PrintableString, but are common in RFC 822 addresses.  The
     abbreviations will ease specification of RFC 822 addresses from
     an X.400 system.  These special encodings shall be interpreted in
     a case insensitive manner, but always generated in lower case.

          A reversible mapping between PrintableString and ASCII can



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     now be defined.  The reversibility means that some values of
     printable string (containing round braces) cannot be generated
     from ASCII.  Therefore, this mapping shall only be used in cases
     where the printable strings have been derived from ASCII (and
     will therefore have a restricted domain).  For example, in this
     specification, it is only applied to a Domain Defined Attribute
     which will have been generated by use of this specification and a
     value such as "(" would not be possible.

          To encode ASCII as PrintableString, the EBNF.ps-encoded
     syntax is used, with all EBNF.ps-restricted-char mapped directly.
     All other 822.CHAR are encoded as EBNF.ps-encoded-char.

          To encode PrintableString as ASCII, parse PrintableString as
     EBNF.ps-encoded, and then reverse the previous mapping.  If the
     PrintableString cannot be parsed, then the mapping is being
     applied in to an inappropriate value, and an error shall be given
     to the procedure doing the mapping. In some cases, it may be
     preferable to pass the printable string through unaltered.

     Some examples are now given.  Note the arrows which indicate
     asymmetrical mappings:

                     PrintableString           ASCII

                     'a demo.'         <->   'a demo.'
                     foo(a)bar         <->   foo@bar
                     (q)(u)(p)(q)      <->   "_%"
                     (a)               <->   @
                     (A)               ->    @
                     (l)a(r)           <->   (a)
                     (126)             <->   ~
                     (                 ->    (
                     (l)               <->   (


     3.5.  RFC 1522

     RFC 1522 defines a mechanism for encoding other character set
     information into elements of RFC 822 Headers.   A gateway may
     ignore this encoding and treat the elements as ASCII.

          A preferred approach is for the gateway to interpret the RFC
     1522 encoding. This will not always be straightforward, because:



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     1.   RFC 1522 permits an openly extensible character set choice,
          which may be broader than T.61.

     2.   It is not always possible to map all characters into the
          equivalent X.400 field.

     RFC 1522 is only applied to fields which are "for information
     only".  A gateway which interprets header elements according to
     RFC 1522 may apply reasonable heuristics to minimise information
     loss.





































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     Chapter 4 - Addressing and Message IDs


     Addressing is the most complex aspect of X.400 <-> RFC 822
     gateway and is therefore  given a separate chapter.  This chapter
     also discusses message identifiers, as they are closely linked to
     addresses.  This chapter, as a side effect, also defines a
     textual representation of an X.400 OR Address.   This
     specification has much similarity to the X.400(92) representation
     of addresses.   This was because early versions of this
     specification were a major input to this work.  This
     specification retains compatibility with earlier versions.  The
     X.400 specification of address representation can be parsed but
     is not generated.

          Initially we consider an address in the (human) mail user
     sense of "what is typed at the mailsystem to reference a mail
     user".  A basic RFC 822 address is defined by the EBNF
     EBNF.822-address:

             822-address     = [ route ] addr-spec

     These definitions are taken from RFC 822.  In SMTP (or another
     822-MTS protocol), the originator and each recipient are
     considered to be defined by such a construct.  In an RFC 822
     header, the EBNF.822-address is encapsulated in the 822-address
     syntax rule, and there may also be associated comments.  None of
     this extra information has any semantics, other than to the end
     user.

          The basic X.400 OR Address, used by the MTS for routing, is
     defined by MTS.ORAddress.  In IPMS, the MTS.ORAddress is
     encapsulated within IPMS.ORDescriptor.

          The RFC 822 822.address is mapped with IPMS.ORDescriptor,
     and that RFC 822 EBNF.822-address is mapped with MTS.ORAddress.

          Section 4.1 defines a textual representation of an OR
     Address, which is used throughout the rest of this specification.
     This text representation is designed to represent an X.400
     address in the LHS (left hand side) or local part of an RFC 822
     address, and so this representation gives a mechanism to
     represent X.400 addresses within RFC 822 addresses.




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          Section 4.2 describes global equivalence mapping between
     parts of the X.400 and RFC 822 name spaces, and defines the
     concept of a MIXER Conformant Global Address Mapping (MCGAM).
     Gateways conforming to this specification shall support MCGAMs.

          Section 4.3 is the core part of this chapter, and defines
     the mapping mechanism.


     4.1.  A textual representation of MTS.ORAddress

     MTS.ORAddress is structured as an ordered set of attributes
     (type/value pairs).  It is clearly necessary to be able to encode
     this in ASCII for gatewaying purposes.  All components shall be
     encoded, in order to guarantee return of error messages, and to
     optimise third party replies.

     4.1.1.  Basic OR Address Representation

     An OR Address has a number of structured and unstructured
     attributes.  For each unstructured attribute, a key and an
     encoding is specified.  For structured attributes, the X.400
     attribute is mapped onto one or more attribute value pairs.  For
     domain defined attributes, each element of the sequence will be
     mapped onto a triple (key and two values), with each value having
     the same encoding.  The attributes are as follows, with 1984
     attributes given in the first part of the attribute key table.
     For each attribute, a reference is given, consisting of the
     relevant sections in X.402 / ISO 10021-2, and the extension
     identifier for 88 only attributes.  The attribute key table
     follows:

       Attribute (Component)                 Key         Enc     Ref     Id

84/88 Attributes

MTS.CountryName                        C                 P     18.3.3
MTS.AdministrationDomainName           ADMD              P     18.3.1
MTS.PrivateDomainName                  PRMD              P     18.3.21
MTS.NetworkAddress                     X121              N     18.3.7
MTS.TerminalIdentifier                 T-ID              P     18.3.23
MTS.OrganizationName                   O                 P/T   18.3.9
MTS.OrganizationalUnitNames.value      OU                P/T   18.3.10
MTS.NumericUserIdentifier              UA-ID             N     18.3.8



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MTS.PersonalName                       PN                P/T   18.3.12
MTS.PersonalName.surname               S                 P/T   18.3.12
MTS.PersonalName.given-name            G                 P/T   18.3.12
MTS.PersonalName.initials              I                 P/T   18.3.12
MTS.PersonalName
   .generation-qualifier               GQ                P/T   18.3.12
MTS.DomainDefinedAttribute.value       DD                P/T   18.1

88 Attributes

MTS.CommonName                         CN                P/T   18.3.2    1
MTS.TeletexCommonName                  CN                P/T   18.3.2    2
MTS.TeletexOrganizationName            O                 P/T   18.3.9    3
MTS.TeletexPersonalName                PN                P/T   18.3.12   4
MTS.TeletexPersonalName.surname        S                 P/T   18.3.12   4
MTS.TeletexPersonalName.given-name     G                 P/T   18.3.12   4
MTS.TeletexPersonalName.initials       I                 P/T   18.3.12   4
MTS.TeletexPersonalName
   .generation-qualifier               GQ                P/T   18.3.12   4
MTS.TeletexOrganizationalUnitNames
   .value                              OU                P/T   18.3.10   5
MTS.TeletexDomainDefinedAttribute
   .value                              DD                P/T   18.1      6
MTS.PDSName                            PD-SERVICE        P     18.3.11   7
MTS.PhysicalDeliveryCountryName        PD-C              P     18.3.13   8
MTS.PostalCode                         PD-CODE           P     18.3.19   9
MTS.PhysicalDeliveryOfficeName         PD-OFFICE         P/T   18.3.14   10
MTS.PhysicalDeliveryOfficeNumber       PD-OFFICE-NUM     P/T   18.3.15   11
MTS.ExtensionORAddressComponents       PD-EXT-ADDRESS    P/T   18.3.4    12
MTS.PhysicalDeliveryPersonName         PD-PN             P/T   18.3.17   13
MTS.PhysicalDeliveryOrganizationName   PD-O              P/T   18.3.16   14
MTS.ExtensionPhysicalDelivery
   AddressComponents                   PD-EXT-DELIVERY   P/T   18.3.5    15
MTS.UnformattedPostalAddress           PD-ADDRESS        UPA   18.3.25   16
MTS.StreetAddress                      PD-STREET         P/T   18.3.22   17
MTS.PostOfficeBoxAddress               PD-BOX            P/T   18.3.18   18
MTS.PosteRestanteAddress               PD-RESTANTE       P/T   18.3.20   19
MTS.UniquePostalName                   PD-UNIQUE         P/T   18.3.26   20
MTS.LocalPostalAttributes              PD-LOCAL          P/T   18.3.6    21








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MTS.ExtendedNetworkAddress
   .e163-4-address.number              NET-NUM           N     18.3.7    22
MTS.ExtendedNetworkAddress
   .e163-4-address.sub-address         NET-SUB           N     18.3.7    22
MTS.ExtendedNetworkAddress
   .psap-address                       NET-PSAP          X     18.3.7    22
MTS.TerminalType                       T-TY              I     18.3.24   23


     The following keys identify different EBNF encodings, which are
     associated with the ASCII representation of MTS.ORAddress.

                        Key         Encoding

                        P     printablestring
                        N     numericstring
                        T     teletex-string
                        P/T   teletex-and-or-ps
                        UPA   upa-string
                        I     labelled-integer
                        X     presentation-address

     The EBNF for presentation-address is taken from the specification
      RFC 1278 "A String Encoding of Presentation Address" [23].

     In most cases, the EBNF encoding maps directly to the ASN.1
     encoding of the attribute.  There are a few exceptions. In cases
     where an attribute can be encoded as either a PrintableString or
     NumericString (Country, ADMD, PRMD), either form is mapped into
     the EBNF.  When generating ASN.1, the NumericString encoding
     shall be used if the string contains digits and only digits.

     There are a number of cases where the P/T (teletex-and-or-ps)
     representation is used.  Where the key maps to a single
     attribute, this choice is reflected in the encoding of the
     attribute (attributes 10-21). For example:

             /CN=yen*{165}/

     For most of the 1984 attributes and common name, there is a
     printablestring and a teletex variant.   This pair of attributes
     is mapped onto the single component here.  This will give a clean
     mapping for the common cases where only one form of the name is
     used.  If there is  teletex attribute or teletex component only,



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     and it contains only characters in the printable string character
     set, it shall be represented in the EBNF as if it had been
     encoded as printable string.   A single printable string
     representation shall also be done when both forms are present and
     they have the same printable string representation.

     The Unformatted Postal Address has a slightly more complex
     mapping onto a variant of   (teletex-and-or-ps), defined as:

     upa-string = [ printable-upa ] [ "*" teletex-string ]
     printable-upa = printablestring *( "|" printablestring )

     The optional teletex part is straightforward.  There is an
     (optional) sequence of printable strings which are mapped in
     order.  For example:

     /PD-ADDRESS=The Dome|The Square|Richmond|England/


          X.400 (1992) has introduced a string representation of OR
     Addresses (see F.401, Annex B).  This has specified a number of
     string keywords for attributes.  As earlier versions of this
     specification  were an input to this work, many of the keywords
     are the same.  To increase compatibility, the following
     alternative values shall be recognised when mapping from RFC 822
     to X.400.  These shall not be generated when mapping from X.400
     to RFC 822.  The following keyword alternative table and the
     subsequent paragraph lists alternative keywords.

                        Keyword         Alternative

                    ADMD              A
                    PRMD              P
                    GQ                Q
                    X121              X.121
                    UA-ID             N-ID
                    PD-OFFICE-NUM     PD-OFFICE NUMBER
                    PD-OFFICE-NUM     PD-OFN
                    PD-EXT-ADDRESS    PD-EA
                    PD-EXT-DELIVERY   PD-ED
                    PD-OFFICE         PD-OF
                    PD-STREET         PD-S
                    PD-UNIQUE         PD-U
                    PD-LOCAL          PD-L



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                    PD-RESTANTE       PD-R
                    PD-BOX            PD-B
                    PD-CODE           PD-PC
                    PD-SERVICE        PD-SN
                    DD                DDA
                    NET-NUM           E.164
                    NET-PSAP          PSAP
                    PD-ADDRESS        PD-A

     When mapping from RFC 822 to X.400, the keywords defined in this
     paragraph shall be recognized.  The ordered keywords: OU1, OU2,
     OU3, and OU4, shall be recognised.  If these are present, no
     keyword OU shall be present.  These will be treated as ordered
     values of OU.  PD-A1, PD-A2, PD-A3, PD-A4, PD-A5, PD-A6 shall be
     treated as ordered lines.  If present, these will be assembled
     with separating line feeds to form a single physical address.  In
     this case PD-ADDRESS (or PD-A) shall not be present.   Similarly,
     there are ordered keywords for domain defined attributes: DD1,
     DD2, DD3, DD4,

          If ISDN is present, it may be interpreted as an E.163/164
     address, using local heuristics to parse the string.  X.400
     defines the key, but does not give an interpretation of the
     value.

          For T-TY (Terminal Type), the X.400 recommended values are
     preferred, but other values are allowed.  These values are: tlx
     (3); ttx (4); g3fax (5); g4fax (6); ia5 (7); and vtx (8).

     4.1.2.  Encoding of Personal Name

     Handling of Personal Name and Teletex Personal Name  is a common
     requirement.   Therefore MIXER defines an alternative to the
     EBNF.standard-type syntax, which utilises the "human" conventions
     for encoding these components.  A syntax is defined, which is
     designed to provide a clean encoding for the common cases of OR
     Address specification where:

     1.   There is no generational qualifier

     2.   Initials, if present, contain only letters

     3.   Given Name, if present, does not contain full stop ("."),
          and is at least two characters long.



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     4.   Surname does not contain full stop in the first two
          characters.

     5    If Surname is the only component, it does not contain full
          stop.

     The following EBNF is defined:

             encoded-pn      = [ given "." ] *( initial "." ) surname

             given           = 2*<ps-char not including ".">

             initial         = ALPHA

             surname         = printablestring

     This is used to map from any string containing only printable
     string characters to an OR address personal name.  To map from a
     string to OR Address components, parse the string according to
     the EBNF.  The given name and surname are assigned directly.  All
     EBNF.initial tokens are concatenated without intervening full
     stops to generate the initials component.

          For an OR address which follows the above restrictions, a
     string is derived in the natural manner.  In this case, the
     mapping will be reversible.

     For example:

             GivenName       = "Marshall"
             Surname         = "Rose"

             Maps with  "Marshall.Rose"

             Initials        = "MT"
             Surname         = "Rose"

             Maps with  "M.T.Rose"

             GivenName       = "Marshall"
             Initials        = "MT"
             Surname         = "Rose"

             Maps with  "Marshall.M.T.Rose"



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     Note that X.400 suggests that Initials is used to encode all
     initials except the surname (X.402 section 18.3.12).  Therefore,
     the defined encoding is "natural" when either GivenName or
     Initials, but not both, are present.  The case where both are
     present can be encoded.

     4.1.3.  Standard Encoding of MTS.ORAddress

     Given this structure, we can specify an EBNF representation of an
     OR Address. The output format of addresses is defined by
     EBNF.std-or-address.  The more flexible input format is defined
     by EBNF.std-or-address-input. The input EBNF has been added
     subsequent to RFC 1327, to reflect the formal incorporation of a
     number of heuristics.  The address element separator on input may
     be "/", ";", or a mixture of these.  The output format is used in
     all examples.

             std-or-address  = 1*( "/" attribute "=" value ) "/"
             attribute       = standard-type
                             / "RFC-822"
                             / dd-key "." std-printablestring



             std-or-address-input =  [ sep pair ] sep  pair *( sep pair )
                                    sep  [ pair sep ]

             sep             = "/" / ";"
             pair            = input-attribute "=" value
             input-attribute = attribute
                             / dd-key ":" std-printablestring
















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             standard-type   = key-string

             dd-key          = key-string

             value           = std-printablestring

             std-printablestring
                             = *( std-char / std-pair )

             std-char        = <"{", "}", "*", and any ps-char
                                             except "/" and "=" >
             std-pair        = "$" ps-char

     For address generation, the standard-type is any key defined in
     the key table in Section 4.1, except PN, and DD.  For address
     parsing, other key values from Section 4.1 are also valid.  The
     EBNF leads to a set of attribute/value pairs. The value is
     interpreted according to the EBNF encoding defined in the table.

          If the standard-type is PN, the value is interpreted
     according to EBNF.encoded-pn, and the components of
     MTS.PersonalName and/or MTS.TeletexPersonalName derived
     accordingly.

          If dd-key is the recognised Domain Defined string (DD) or
     one of the alternatives defined in Section 4.1, then the type and
     value are interpreted according to the syntax implied from the
     encoding, and aligned to either the teletex or printable string
     form.  Key and value shall have the same encoding.

          If value is "RFC-822", then the (printable string) Domain
     Defined Type of "RFC-822" is assumed.  This is an optimised
     encoding of the domain defined type defined by this
     specification.

          The matching of all keywords shall be done in a case-
     independent manner.

          EBNF.std-or-address uses the characters "/" and "=" as
     delimiters.  Domain Defined Attributes and any value may contain
     these characters.  A quoting mechanism, using the non-printable
     string "$" is used to allow these characters to be represented.



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          If an address of this syntax is parsed, and a country value
     is present, but no ADMD, the string shall be interpreted as if an
     ADMD value of single space had been specified.

     4.2.  Global Address Mapping

     From a user perspective, the ideal mapping  would be entirely
     symmetrical and global, to enable addresses to be referred to
     transparently in the remote system, with the choice of gateway
     being left to the Message Transfer Service.  There are two
     fundamental reasons why this is not possible:

     1.   The syntaxes are sufficiently different to make this
          impossible.

     2    There is insufficient administrative co-operation between
          the X.400 and RFC 822 name registration authorities for this
          to work.

     Another way to view this situation is to see that there is not a
     full global equivalence between X.400 and RFC 822 addressing.  To
     meet user needs to the extent possible, this specification
     provides for equivalence where there is sufficient co-operation.
     To be useful, this equivalence shall be recognised and
     interpreted in the same way by all gateways.  Therefore, an
     asymmetrical mapping is defined, which can be symmetrical where
     there is appropriate administrative co-operation.  Section 4.3
     describes the asymetrical aspects.   This section describes a
     mechanism to enable the administrative co-ordination for
     symmetrical mappings.

          In order to achieve a symmetrical mapping there is a need to
     define an administrative equivalence between parts of the OR
     Address and Domain namespaces.  Previous version of this
     specification did this by definition of a global set of mappings.
     MIXER defines the concept of a MIXER Conformant Global Address
     Mapping (MCGAM).  This acronym is defined so that it is very
     clear what is being referenced.

          The X.400 and Internet Mail address spaces are hierarchical.
     It is possible to define an equivalence between two points in the
     hierarchies, such that addresses below that point can be derived
     in an algorithmic manner.  An MCGAM is a mapping from a point in
     one hierarchy to a point in the other hierarchy.  An "MGGAM pair"



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     is a pair of symmetrical mappings between two points.  To define
     an MCGAM, the following shall apply:

     1.   The authority defining the MCGAM shall have responsibility
          for BOTH of the namespaces between which the MCGAM is
          defined.

     2.   The authority defining the MCGAM is responsible to ensure
          that addresses allocated below the two equivalence points
          conform to the rules set out below.

     3.   The authority defining the MCGAM is responsible to ensure
          that addresses which are generated according to the MCGAM
          are routed correctly.

     In general, MCGAMs will be independent.   In some cases, a set of
     MCGAMs may be related (e.g., where one MCGAM defines a mapping
     for an organization and a second MCGAM defines an excpetion for a
     subtree within the organization).   In this case, the related set
     of MCGAMs shall be treated as a single MCGAM for distribution
     purposes.

          The existence of an MCGAM does not imply routability and
     access for all users.

          The authority defining an MCGAM may simply use this mapping
     locally.  This will often be the case in a "local scenario"
     gateway.   Because of third party addressing, a MIXER gateway
     will work best with the maximum number of MCGAMs.   Therefore,
     three mechanisms are defined to enable publication and exchange
     of MCGAMs:

     1.   Distribution of text tables.  This is described in Appendix
          F of this specification.

     2.   Distribution by Domain Name Service.   This is described in
          RFC 1664bis [3].

     3.   Distribution by X.500 Directory Service.   This is defined
          in RFC 1838 [26].

          The following sections define how the MCGAM namespace
     equivalence is modelled.  The Internet Domain Namespace defines a
     simple hierarchy.   For the purposes of this mapping, only parts



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     of the namespace where domains conform to the EBNF domain-syntax
     are allowed.

             domain-syntax   = alphanum [ *alphanumhyphen alphanum ]
             alphanum        = <ALPHA or DIGIT>
             alphanumhyphen  = <ALPHA or DIGIT or HYPHEN>


     Although RFC 822 allows for a more general syntax, this
     restricted syntax is used in MIXER as it is the one chosen by the
     various domain service administrations.  In practice, it reflects
     all RFC 822 usage.

          The following OR Address attributes are considered as a
     hierarchy, and may be specified by the domain.  They are (in
     order of the hierarchy defined by MIXER):

             Country, ADMD, PRMD, Organization, Organizational Units

     There may be up to four ordered Organizational Units.   This
     hierarchy reflects most usage of X.400, although X.400 may be
     used in other ways. In particular, it covers the Mnemonic OR
     Address using a 1984 compatible encoding.  This is seen as the
     dominant form of OR Address. MCGAMs may only be used when this
     hierarchy applies.

          An equivalence mapping is defined between two nodes in the
     respective hierarchies. For example:

             => "AC.UK" might be mapped with
             PRMD="UK.AC", ADMD="GOLD 400", C="GB"

     The mapping identifies that the management of these points in the
     respective hierarchies is the same (or co-operate very closely).
     The equivalence means that the namespaces below this equivalence
     point map 1:1, except where the mapping is overridden by further
     equivalence mappings lower down the hierarchy.   This equivalence
     may be achieved in three ways:

     1.   All of the nodes below this point are RFC 822, and the MIXER
          mapping defines the X.400 addresses for these nodes.

     2.   All of the nodes below this point are X.400, and the MIXER
          mapping defines the  RFC 822 addresses for these nodes.



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     3.   There are X.400 and RFC 822 nodes below this point, and
          addressing is managed in a manner which  ensures the
          equivalence.   The rules to achieve this are  defined by
          MIXER.

     Each of these ways gives a framework for MCGAM definition.

          When an MCGAM is defined, a systematic mapping for the
     inferior nodes in the two hierarchies follows.   This is a 1:1
     mapping between the nodes in the subtrees.  For example, given
     the MCGAM pair defined above:

             the domain "R-D.Salford.AC.UK" algorithmically maps with
             OU="R-D", O="Salford", PRMD="UK.AC", ADMD="GOLD 400", C="GB"


     Note that when an equivalence is defined, that this can be re-
     defined for lower points in the hierarchy.   However, it is not
     possible to declare contained subtrees to be un-mappable.

          The equivalence mapping also provides a mechanism to deal
     with missing elements in the X.400 hierarchy (most commonly the
     PRMD, which is the only element that may be ommitted when
     conforming to recent versions of X.400).  A domain may be
     associated with an omitted attribute in conjunction with several
     present ones.  When performing the algorithmic insertion of
     components lower in the hierarchy, the omitted value shall be
     skipped.  For example:

             If there is an MCGAM pair between domain HNE.EGM" and
             "O=HNE", "ADMD=ECQ", "C=TC", and omitted PRMD

     then

             "ZI.HNE.EGM" is algorithmically mapped with
             "OU=ZI", "O=HNE", "ADMD=ECQ", "C=TC"

     Attributes may have null values, and  this is treated separately
     from omitted attributes (while it is not ideal
      to make this distinction, it is useful in practice).

     4.2.1.  Directory and Nameserver Mappings

     When a set of MCGAMs are supported by X.500 or DNS, there is the



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     possibility that results will be indeterminate due to timeout.
     Lookup shall be repeated until a value is determined, in order to
     maintain  consistent gateway operation.

          Where the mapping relates to an envelope address, the
     gateway shall non-deliver messages according to the associated
     MTA's normal timeout policy.  Where the mapping relates to
     addresses in the message header, there shall be a timeout in the
     range of 1-4 hours or shorter if this is required to maintain
     quality of service constraints.   If a mapping cannot be done in
     this time, address encapsulation shall be used.

     4.3.  EBNF.822-address <-> MTS.ORAddress

     This section defines the basic address mapping.

     4.3.1.  X.400 encoded in RFC 822

     This section defines how X.400 addresses are represented in RFC
     822 addresses.

          The std-or-address syntax is  used to encode OR Address
     information in the 822.local-part of EBNF.822-address.  Where
     there is an applicable equivalence mapping, further  OR Address
     information is associated with the 822.domain component.  This
     cannot be used in the general case, due to character set
     problems, and to the variants of X.400 OR Addresses which use
     different attribute types.  The only way to encode the full
     PrintableString character set in a domain is by use of the
     822.domain-ref syntax (i.e. 822.atom).  This is likely to cause
     problems on many systems.  The effective character set of domains
     is in practice reduced from the RFC 822 set, by restrictions
     imposed by domain conventions and policy [10], and by the EBNF
     definition in SMTP.

          A generic 822.address consists of a 822.local-part and a
     sequence of 822.domains (e.g., <@domain1,@domain2:user@domain3>).
     All except the 822.domain associated with the 822.local-part
     (domain3 in this case) are considered to specify routing within
     the RFC 822 world, and will not be interpreted by the gateway
     (although they may have identified the gateway from within the
     RFC 822 world).

          The  822.domain associated with the 822.local-part



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     identifies the gateway from within the RFC 822 world.  This final
     822.domain may be used to determine some number of OR Address
     attributes, where this does not conflict with the first role.
     RFC 822 routing to gateways will usually be set up to facilitate
     the 822.domain being used for both purposes.

          In the case that there is no applicable equivalence mapping,
     all of the X.400 address is encoded in the 822.local-part and the
     822.domain identifies the gateway to which the message is being
     sent.  This technique may be used by the RFC 822 user for any
     X.400 address where the equivalence mapping is not known.

          In the case that there is an applicable MCGAM, the maximum
     number of attributes are encoded in the 822.domain.  The
     remaining attributes are encoded on the LHS, using the
     EBNF.std-or-address syntax.  For example:

             /I=J/S=Linnimouth/GQ=5/@Marketing.Widget.COM

     encodes the MTS.ORAddress consisting of:

             MTS.CountryName                       = "TC"
             MTS.AdministrationDomainName          = "BTT"
             MTS.OrganizationName                  = "Widget"
             MTS.OrganizationalUnitNames.value     = "Marketing"
             MTS.PersonalName.surname              = "Linnimouth"
             MTS.PersonalName.initials             = "J"
             MTS.PersonalName.generation-qualifier = "5"

     on the basis of an MCGAM pair between:

             Domain: Widget.COM
             OR Address: O="Widget", ADMD="BTT", C="TC"

     Given the OR address, the domain Widget.COM is determined from
     the equivalence mapping and the next component is determined
     algorithmically to give Marketing.Widget.COM.  The remaining
     attributes are encoded on the LHS in 822.local-part.

          There is a further mechanism to simplify the encoding of
     common cases, where the only attributes to be encoded on the LHS
     are (non-Teletex) Personal Name attributes which comply with the
     restrictions of 4.1.2.  To achieve this, the 822.local-part shall
     be encoded as EBNF.encoded-pn.  In the previous example, if the



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     GenerationQualifier was not present in the OR Address, it would
     map with the RFC 822 address:  J.Linnimouth@Marketing.Widget.COM.

          From the standpoint of the RFC 822 Message Transfer System,
     the domain specification is used to route the message in the
     standard manner.  The standard domain mechanisms are used to
     select appropriate gateways for the corresponding OR Address
     space.  It is the responsibility of the management that defines
     the equivalence mapping to define routing in the manner which
     will enable the message to be delivered.

     4.3.2.  RFC 822 encoded in X.400

     The previous section showed a mapping from X.400 to RFC 822.  In
     the case where  the mapping was symmetrical and based on the
     equivalence mapping, this has also shown how RFC 822 is encoded
     in the X.400.   This equivalence cannot be used for all RFC 822
     addresses.

          The general case is mapped by use of domain defined
     attributes.  A (Printable String) Domain defined type "RFC-822"
     is defined. The associated attribute value is an ASCII string
     encoded according to Section 3.3.3 of this specification. The
     interpretation of the ASCII string follows RFC 822, and RFC 1123
     [10,16].  Domains shall always be fully qualified.

          Other OR Address attributes will be used to identify a
     context in which the OR Address will be interpreted.  This might
     be a Management Domain, or some part of a Management Domain which
     identifies a gateway MTA.  For example:

             C               = "GB"
             ADMD            = "GOLD 400"
             PRMD            = "UK.AC"
             O               = "UCL"
             OU              = "CS"
             "RFC-822"      =  "Jimmy(a)WIDGET-LABS.CO.UK"

     OR

             C               = "TC"
             ADMD            = "Wizz.mail"
             PRMD            = "42"
             "rfc-822"       = "postel(a)venera.isi.edu"



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     Note in each case the PrintableString encoding of "@" as "(a)".
     In the second example, the "RFC-822" domain defined attribute is
     interpreted everywhere within the (Private) Management Domain.
     In the first example, further attributes are needed within the
     Management Domain to identify a gateway.  Thus, this scheme can
     be used with varying levels of Management Domain co-operation.

          There is a limit of 128 characters in the length of value of
     a domain defined attribute, and an OR Address can have a maxmimum
     of four domain defined attributes.  Where the printable string
     generated from the RFC 822 address exceeds 128 characters,
     additional domain defined attributes are used to enable up to 512
     characters to be encoded.  These attributes shall be filled
     completely before the next one is started.   The (Printable
     String) DDA keywords are:  RFC822C1; RFC822C2; RFC822C3.  Longer
     addresses cannot be encoded.

          MIXER defines a representation of RFC 822 addresses in
     printable string domain defined attributes.  Teletex domain
     defined attributes with a key of RFC-822, RFC822C1; RFC822C2;
     RFC822C3 shall not be generated.  This is for backwards
     compatibility reasons.

          Reception of these attributes in the manner defined below is
     mandatory.  This is to allow the possibility for future versions
     of MIXER to allow generation of teletex domain defined
     attributes.  Where the values of all of these teletex domain
     defined attributes are printable string characters, they shall be
     interpreted in the same way as the printable string domain
     defined attributes.   If this is not the case, the printable
     string encoding translation shall be omitted.  If both teletex
     and printable string attributes are present, this is valid if and
     only if they represent exactly the same RFC 822 address.

     4.3.3.  Component Ordering

     In most cases, ordering of OR Address components is not
     significant for the mappings specified.  However, Organizational
     Units (printable string and teletex forms) and Domain Defined
     Attributes are specified as SEQUENCE in MTS.ORAddress, and so
     their order may be significant.  This specification needs to take
     account of this:

     1.   To allow consistent mapping into the domain hierarchy



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     2.   To ensure preservation of order over multiple mappings.

     There are three places where an order is specified:

     1.   The text encoding (std-or-address) of MTS.ORAddress as used
          in the local-part of an RFC 822 address.  An order is needed
          for those components which may have multiple values
          (Organizational Unit, and Domain Defined Attributes). When
          generating an 822.std-or-address, components of a given type
          shall be in hierarchical order with the most significant
          component on the RHS (right hand side or domain part).  If
          there is an Organization Attribute, it shall be to the right
          of any Organizational Unit attributes.  These requirements
          are for the following reasons:

     -         Alignment to the hierarchy of other components in RFC
               822 addresses (thus, Organizational Units will appear
               in the same order, whether encoded on the RHS or LHS).

     -         Backwards compatibility with RFC 987/1026.

     -         To ensure that gateways generate consistent addresses.
               This is both to help end users, and to generate
               identical message ids.

          Further, it is recommended that all other attributes are
          generated according to this ordering, so that all attributes
          so encoded follow a consistent hierarchy.   When generating
          822.msg-id, this order shall be followed.

     2.   For the Organizational Units (OU) in MTS.ORAddress, the
          first OU in the SEQUENCE is the most significant, as
          specified in X.400.

     3.   For the Domain Defined Attributes in MTS.ORAddress, the
          First Domain Defined Attribute in the SEQUENCE is the most
          significant.

          Note that although this ordering is mandatory for this
          mapping, MIXER does not give additional implications on the
          ordering significance within X.400.






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     4.3.4.  RFC 822 -> X.400 Basic Address Mapping

     There are two basic cases:

     1.   X.400 addresses encoded in RFC 822.  This will also include
          RFC 822 addresses which are given reversible encodings.

     2.   "Genuine" RFC 822 addresses.

     The mapping shall proceed as follows, by first assuming case 1).

     STAGE I.

     1.   If the 822-address is not of the form:

                  local-part "@" domain

          take the domain which will be routed on and apply step 2 of
          stage 1 to derive (a possibly null) set of attributes. Then
          go to stage II.

          The gateway may  reduce a source route address to this form
          by removal of all but the last domain.  In terms of the
          design intentions of RFC 822, this would be an incorrect
          action. (Note that an address of the form local%part@domain
          is not a source route).  However, in most cases, it will
          provide a better service to the end user, and is in line
          with the Internet Host Requirements.  This is a reflection
          on the common inappropriate use of source routing in RFC 822
          based systems, despite the discussion in the Host
          Requirements [10].  Either approach, or the intermediate
          approach of stripping only domain references which reference
          the local gateway are conformant to this specification.

     2.   If the 822.local-part uses the 822.quoted-string encoding,
          remove this quoting.  If the resulting unquoted
          822.local-part has leading space, trailing space, or two
          adjacent spaces go to stage II.

     3.   If the unquoted 822.local-part contains any characters not
          in PrintableString, "{", "}", "*", and "$", go to stage II.

     4.   Parse the (unquoted) 822.local-part according to the EBNF
          EBNF.std-or-address-input.  Checking of upper bounds shall



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          not be done at this point.  If this parse fails, parse the
          local-part according to the EBNF EBNF.encoded-pn.  If this
          parse fails, go to stage II.  The result is a set of
          type/value pairs.

     5.   Associate the EBNF.attribute-value syntax (determined from
          the identified type) with each value, and check that it
          conforms.  If not, go to stage II.

     6.   If the set of attributes forms a valid X.400 address,
          according to X.402, then go to step 9.  All forms of X.400
          address are allowed at this stage.  Steps 7-8 default
          attributes for certain types of OR Address.

     7.   If the set of attributes cannot form a mnemonic form of
          X.400 address after addition of attributes which may be
          derived from the EBNF.domain (C, ADMD, PRMD, O, OU), go to
          stage II.

     8.   Attempt to parse EBNF.domain as:

                  *( domain-syntax "." ) known-domain

          Where EBNF.known-domain is the longest possible match in the
          set of MCGAMs being used by the gateway (described in
          Section 4.2).  EBNF.domain-syntax is the restricted domain
          syntax defined in Section 4.2, to which all of the domain
          components shall conform for the parse to be successful.  If
          this fails, go to stage II.

          For each component, systematically allocate the attribute
          implied by each EBNF.domain-syntax component in the order:
          C, ADMD, PRMD, O, OU.  Note that if the MCGAM used
          identifies an "omitted attribute", then this attribute shall
          be omitted in the systematic allocation.  If this new
          component exceed an upper bound (ADMD: 16; PRMD: 16; O: 64;
          OU:  32) or it would lead to more than four OUs, then go to
          stage II with the attributes derived.

          The attributes derived in this step (referred to as RHS
          attributes)
           are merged with the ones derived from the LHS (step 6).
          In some cases, not all of the RHF attributes are used.  LHS
          attributes are all used.  C will not be in the LHS



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          attributes.  If ADMD is in the LHS attributes,  only C is
          taken from the RHS attributes. If PRMD is in the LHS
          attributes, C and ADMD are taken from the RHS attributes.
          If O is on the LHS, C, ADMD and PRMD (if present) are taken
          from the RHS attributes.  In other cases all RHS attributes
          are taken.

     9.   Ensure that the set of attributes conforms both to the
          MTS.ORAddress specification and to the restrictions on this
          set given in X.400, and that no upper bounds are exceeded
          for any attribute.  If not go to stage II.

     10.  Build the OR Address from this information.


     STAGE II.

     This will only be reached if the RFC 822 EBNF.822-address is not
     a valid X.400 encoding.  This implies that the address  refers to
     a recipient on an RFC 822 system or that the encoding of the
     address is invalid.  Such addresses shall be encoded in an X.400
     OR Address using a domain defined attribute.

     1.   Convert the EBNF.822-address to PrintableString, as
          specified in Chapter 3.

     2.   Generate the "RFC-822" domain defined attribute  from this
          string.

     3.   Build the rest of the OR Address in the manner described
          below.

     It is not always possible to encode the domain defined attribute
     due to length restrictions.  If the limit is exceeded by a
     mapping at the MTS level, then the gateway shall reject the
     message in question.  If this occurs at the IPMS level, then the
     action will depend on the policy being taken for IPMS encoding,
     which is discussed in Section 5.1.3.

     Use Stage I, step 8, to generate a set of attributes to build the
     remainder of the address.  The administrative equivalence of the
     mappings will ensure correct routing through X.400 to a gateway
     back to RFC 822.




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          If Stage I, step 8 does not generate a set of attributes or
     the address generated is unroutable, the remained of the OR
     address is generated as follows.  The remainder of the OR address
     effectively identifies a source route to a gateway from the X.400
     side.  There are three cases, which are handled differently:

     SMTP Return Address
          This shall be set up so that errors are returned through the
          same gateway.  Therefore, the OR Address of the local
          gateway shall be used.

     IPMS Addresses
          These are optimised for replying.  In general, the message
          may end up anywhere within the X.400 world, and so this
          optimisation identifies a gateway appropriate for  the RFC
          822 address being converted.  The 822.domain to which the
          address would be routed is used to select an appropriate
          gateway.

          In this case, it may be useful to use a non-local gateway,
          which will optimise the reply address.   This information
          may be looked up in gateway tables in a manner equivalent to
          the MCGAM lookup.  Because of the similarity of lookup, the
          three MCGAM lookup mechansims (table, X.500, DNS) are also
          available to look up this information.   This information is
          local, and a gateway may insert any appropriate  (gateway)
          OR Address.  The longest possible match on the 822.domain
          defines which gateway to use.  This mechanism is used for
          any part of the X.400 namespace for which it is desirable to
          identify a preferred X.400 gateway in order to optimise
          routing.

          If no mapping is found for the 822.domain, a default value
          (typically that of the local gateway) is used.  It is never
          appropriate to ignore the locally used MCGAMs.

     SMTP Recipient
          As the RFC 822 and X.400 worlds are in principle fully
          connected, there is no technical reason for this situation
          to occur. In practice, this is not the case.  In some cases,
          routing may be configured to use X.400 to connect an RFC 822
          island to the Internet.  The information that this part of
          the domain space is to be routed by X.400 rather than
          remaining within the RFC 822 world shall be configured



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          privately into the gateway in question. X.400 routing shall
          not make use of the presence of the RFC-822 DDA to perform
          X.400 routing.  The OR address shall then be generated in
          the same manner as for an IPMS address, using the locally
          available MCGAMs.  It is to support this case that the
          definition of the global domain to gateway mapping is
          important, as the use of this mapping will lead to a remote
          X.400 address, which can be routed by X.400 routing
          procedures.  The information in this mapping shall not be
          used as a basis for deciding to convert a message from RFC
          822 to X.400.

     Three examples are given, neither of which has applicable MCGAMs.

     Example 1: (Address not in "localpart" "@" "domainpart")

     @relay.co.uk:userb@host2
         maps to
     c=gb; a= ; p=uk.ac; o=mr; dd.rfc-822=(a)relay.co.uk:userb(a)host2;

     Example 2: (Address with non printablestring characters)

     Tom_Harris@cs.widget.com
          maps to
     c=us; a=MCI; P=relay; dd.rfc-822=Tom(u)Harris(a)cs.widget.com;


     Example 3: (Address with an entry for alter.net into the OR Address
     of Preferred Gateway table, pointing to c=gb; A=BTglobal; P=relay)

     postmaster@UK.alter.net
     maps to
     c=gb; a=BTglobal; P=relay; dd.rfc-822=postmaster(a)UK.alter.net;


     4.3.4.1.  Heuristic for mapping RFC 822 to X.400

     The following heuristic, which  relates to ordering of address
     components, may be used when mapping from RFC 822 to X.400.  The
     ordering of attributes may be inverted or mixed, and so the
     following heuristics may be applied:

          If there is an Organization attribute to the left of any Org
          Unit attribute, assume that the hierarchy is inverted.  This



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          is to facilitate the situation where a user has input the
          attributes in reverse hierarchical order.  To do this the
          gateway shall first map according to the order defined in
          4.3.3.    If this mapping generates an address which X.400
          address verification shows to be invalid, this heuristic may
          be applied as an alternative to immediate rejection of the
          address.

     4.3.5.  X.400 -> RFC 822 Basic Address Mapping


     There are two basic cases:

     1.   RFC 822 addresses encoded in X.400.

     2.   "Genuine" X.400 addresses.  This may include symmetrically
          encoded RFC 822 addresses.

     When an MTS Recipient OR Address is interpreted, gatewaying will
     be selected if there is a single "RFC-822" domain defined
     attribute present.  In this case, use mapping A and in other
     cases, use mapping B.

          RFC 1327 specified that this shall only be done when the
     gateway identfied is local or otherwise known, and identified the
     approach specified here as a pragmatic option.  Experience has
     shown that this is effective in practice, despite theoretical
     problems.

          If a gateway wishes to make a mapping in a manner similar to
     RFC 1327, but does not wish for this global interpretation (e.g.,
     to support an RFC 822 local system, which does not use global
     addressing), then it may choose a private domain defined
     attribute, different to "RFC-822".  An RFC 1327 gateway might be
     configurable to operate in this manner.

     Mapping A

     1.   Map the domain defined attribute value to ASCII, as defined
          in Chapter 3, and drop all other attributes.

     Mapping B.

     This is used for X.400 addresses which do not use the explicit



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     RFC 822 encoding.

     1.   For all string encoded attributes, remove any leading or
          trailing spaces, and replace adjacent spaces with a single
          space.

          The only attribute which is permitted to have zero length is
          the ADMD.  This shall be mapped onto a single space.

          These transformations are for lookup only.   If an
          EBNF.std-or-address mapping is used as in 4), then the
          original values shall be used.

     2.   The numeric country codes may be mapped to the two letter
          values (as defined in ISO 3166).  Global mappings are
          usually only defined in terms of the ISO 3166 codes.

     3.   Noting the hierarchy specified in 4.3.1 and including
          omitted attributes, determine the maximum set of attributes
          which have an associated domain specification in the local
          set of MCGAMs.  If no match is found, allocate the domain as
          described below, and go to step 5. The default domain to be
          used is the specification of the local gateway.   A gateway
          may use other domains according to private mapping tables or
          heuristics.   For example, it may choose a domain which it
          knows to provide a free gateway service to the mapped
          address.

          In cases where the address refers to an X.400 UA, it is
          important that the generated domain will correctly route to
          a gateway.  In general, this is achieved by carefully co-
          ordinating RFC 822 routing with the definition of the
          MCGAMs, as there is no easy way for the gateway to make this
          check.  One rule that shall be used is that domains with
          only one component will not route to a gateway.  If the
          generated domain does not route correctly, the address is
          treated as if no match is found.

          The gateway may also make use of a mapping equivalent to the
          MCGAM mapping to determine the domain to use.  This mapping
          is done from the OR Address hierarchy.   This is not a
          global mapping, but is a routing style mapping from the OR
          Address space, to enable a best choice domain to be
          inserted.   This mapping is supported by the three MCGAM



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          lookup mechanisms.

     4.   The mapping identified  in 3) gives a domain, and an OR
          address prefix.  Follow the hierarchy: C, ADMD, PRMD, O, OU.
          For each successive component below the OR address prefix,
          which conforms to the syntax EBNF.domain-syntax (as defined
          in 4.3.1), allocate the next subdomain.  At least one
          attribute of the X.400 address shall not be mapped onto
          subdomain, as 822.local-part cannot be null.  If there are
          omitted attributes in the OR address prefix, these will have
          correctly and uniquely mapped to a domain component.   Where
          there is an attribute omitted below the prefix, all
          attributes remaining in the OR address shall be encoded on
          the LHS.  This is to ensure a reversible mapping. For
          example, if there is an address /S=XX/O=YY/ADMD=A/C=NN/ and
          a mapping for /ADMD=A/C=NN/ is used, then /S=XX/O=YY/ is
          encoded on the LHS.

     5.   If the address contains any attribute not used in mnemonic
          form, then all of the attributes in the address shall be
          encoded on the LHS in EBNF.std-or-address syntax, as
          described below.

          For addresses of mnemonic form, if the remaining components
          are personal-name components, conforming to the restrictions
          of 4.2.1, then EBNF.encoded-pn is derived to form
          822.local-part.  In other cases the remaining components are
          simply encoded as 822.local-part using the
          EBNF.std-or-address syntax.  If necessary, the
          822.quoted-string encoding is used.  The following are
          examples of legal quoting: "a b".c@x; "a b.c"@x.  Either
          form may be generated.  Generation of the latter style is
          strongly recommended.

     Four examples are given.

     Example 1: (Address with missing X.400 elements and no specific
     mapping rule for "o=sales; a=Master400; C=it", where a mapping
     exists for a=master400; C-it;)

     S=Support; O=sales;  A=Master400; C=it;
         maps to
     /S=Support/o=sales/@Master400.it




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     Example 2: (Address with illegal characters in RFC822 generated
     domain if default hierarchical translation (specific mapping rule
     is existing for c=fr; a=atlas; p=autoroutes) is used)

     S=renseignements; O=Region Parisienne; P=autoroutes; A=atlas; C=fr;
         maps to
     "/S=renseignements/o=Region Parisienne/"@autoroutes.fr

     Example 3:  (Address containing elements not mappable into RFC822
     local part)

     S=Rossi; DD.cap=20100; DD.ph1=Via Larga 11;
     DDA.city=Milano;  A=PtPostel; C=it;

         maps to

     "/DD.cap=20100/DD.ph1=Via Larga 11/DD.city=Milano/S=Rossi/"@ptpostel.it


     Example 4:   (Address with an entry for A=ATT; C=us; into the domain
     of Preferred Gateway table, pointing to attmail.com)

     G=Andy; S=Wharol; O=MMNY; A=ATT; C=us;

     maps to

     /G=Andy/S=Wharol/O=MMNY


     4.4.  Repeated Mappings

     There are two types of repeated mapping:

     1.   A recursive mapping, where the repeat is within one gateway

     2    A source route, where the repetition occurs across multiple
          gateways

     4.4.1.  Recursive Mappings

     It is possible to supply an address which is recursive at a
     single gateway.  For example:





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             C          = "XX"
             ADMD       = "YY"
             O          = "ZZ"
             "RFC-822"  = "Smith(a)ZZ.YY.XX"

     This is mapped first to an RFC 822 address, and then back to the
     X.400 address:

             C          = "XX"
             ADMD       = "YY"
             O          = "ZZ"
             Surname    = "Smith"

     In some situations this type of recursion may be frequent.  It is
     important where this occurs, that no unnecessary protocol
     conversion occurs. This will minimise loss of service.

     4.4.2.  Source Routes

     The mappings defined are symmetrical and reversible across a
     single gateway.  The symmetry is particularly useful in cases of
     (mail exploder type) distribution list expansion.  For example,
     an X.400 user sends to a list on an RFC 822 system which he
     belongs to.  The received message will have the originator and
     any 3rd party X.400 OR Addresses in correct format (rather than
     doubly encoded).  In cases (X.400 or RFC 822) where there is
     common agreement on gateway identification, then this will apply
     to multiple gateways.

          When a message traverses multiple gateways, the mapping will
     always be reversible, in that a reply can be generated which will
     correctly reverse the path.  In many cases, the mapping will also
     be symmetrical, which will appear clean to the end user.  For
     example, if countries "AB" and "XY" have RFC 822 networks, but
     are interconnected by X.400, the following may happen:  The
     originator specifies:

             Joe.Soap@Widget.PTT.XY

     This is routed to a gateway, which generates:






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             C               = "XY"
             ADMD            = "PTT"
             PRMD            = "Griddle MHS Providers"
             Organization    = "Widget Corporation"
             Surname         = "Soap"
             Given Name      = "Joe"

     This is then routed to another gateway where the mapping is
     reversed to give:

             Joe.Soap@Widget.PTT.XY

     Here, use of the gateway is transparent.

          Mappings will only be symmetrical where mapping equivalences
     are defined. In other cases, the reversibility is more important,
     due to the (far too frequent) cases where RFC 822 and X.400
     services are partitioned.

          The syntax may be used to source route.  THIS IS STRONGLY
     DISCOURAGED.  For example:

             X.400 -> RFC 822  -> X.400

             C             = "UK"
             ADMD          = "Gold 400"
             PRMD          = "UK.AC"
             "RFC-822"     = "/PN=Duval/DD.Title=Manager/(a)Inria.ATLAS.FR"

     This will be sent to an arbitrary UK Academic Community gateway
     by X.400.  Then it will be sent by JNT Mail to another gateway
     determined by the domain Inria.ATLAS.FR (FR.ATLAS.Inria).  This
     will then derive the X.400 OR Address:

             C             = "FR"
             ADMD          = "ATLAS"
             PRMD          = "Inria"
             PN.S          = "Duval"
             "Title"       = "Manager"







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     Similarly:
     RFC 822 -> X.400 -> RFC 822

     "/RFC-822=jj(a)seismo.css.gov/PRMD=AC/ADMD=BT/C=GB/"@monet.berkeley.edu

     This will be sent to monet.berkeley.edu by RFC 822, then to the
     AC PRMD by X.400, and then to jj@seismo.css.gov by RFC 822.

     4.5.  Directory Names

     Directory Names are an optional part of OR Name, along with OR
     Address.  The RFC 822 addresses are mapped onto the OR Address
     component. As there is no functional mapping for the Directory
     Name on the RFC 822 side, a textual mapping is used.  There is no
     requirement for reversibility in terms of the goals of this
     specification.  There may be some loss of functionality in terms
     of third party recipients where only a directory name is given,
     but this seems preferable to the significant extra complexity of
     adding a full mapping for Directory Names.

          The Directory Name shall be represented within an RFC 822
     comment using the comaptible formats of RFC 1484 or RFC 1485.  It
     is recommended that the directory string format of RFC 1485 is
     used [24].  The User Friendly Name form of RFC 1484 may be used
     [25].

     4.6.  MTS Mappings

     The basic mappings at the MTS level are:

     1) SMTP originator ->
                   MTS.PerMessageSubmissionFields.originator-name
        MTS.OtherMessageDeliveryFields.originator-name ->
                   SMTP originator

     2) SMTP recipient ->
                   MTS.PerRecipientMessageSubmissionFields
        MTS.OtherMessageDeliveryFields.this-recipient-name ->
                   SMTP recipient

     SMTP recipients and return addresses are encoded as
     EBNF.822-address.

          The MTS Originator is always encoded as MTS.OriginatorName,



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     which maps onto MTS.ORAddressAndOptionalDirectoryName, which in
     turn maps onto MTS.ORName.

     4.6.1.  RFC 822 -> X.400 MTS Mappings

     From the SMTP Originator, use the basic ORAddress mapping, to
     generate MTS.PerMessageSubmissionFields.originator-name
     (MTS.ORName), without a DirectoryName.

          For recipients, the following settings are made for each
     component of MTS.PerRecipientMessageSubmissionFields.

     recipient-name
          This is derived from the SMTP recipient by the basic
          ORAddress mapping.

     originator-report-request
          This may either be set to "delivery-report", or set
          according to SMTP extensions as set out in Appendix A.

     explicit-conversion
          This optional component is omitted, as this service is not
          needed

     extensions
          The default value (no extensions) is used

     4.6.2.  X.400 -> RFC 822 MTS Mappings

     The basic functionality is to generate the SMTP originator and
     recipients.  There is information present on the X.400 side,
     which cannot be mapped into analogous SMTP services.  For this
     reason, new RFC 822 fields are added for the MTS Originator and
     Recipients.  The information discarded at the SMTP level will be
     present in these fields. In some cases a (positive) delivery
     report will be generated.

     4.6.2.1.  SMTP Mappings

     Use the basic ORAddress mapping, to generate the SMTP originator
     (return address) from
     MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName).  If
     MTS.ORName.directory-name is present, it is discarded.  (Note
     that it will be presented to the user, as described in 4.6.2.2).



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          The mapping  uses the MTA level information, and maps each
     value of MTA.PerRecipientMessageTransferFields.recipient-name,
     where the responsibility bit is set, onto an SMTP recipient.

     Note:The SMTP recipient is conceptually generated from
          MTS.OtherMessageDeliveryFields.this-recipient-name.  This is
          done by taking
          MTS.OtherMessageDeliveryFields.this-recipient-name, and
          generating an SMTP recipient according to the basic
          ORAddress mapping, discarding MTS.ORName.directory-name if
          present.  However, if this model was followed exactly, there
          would be no possibility to have multiple SMTP recipients on
          a single message.  This is unacceptable, and so layering is
          violated.

     4.6.2.2.  Generation of RFC 822 Headers

     Not all per-recipient information can be passed at the SMTP
     level.  For this reason, two new RFC 822 headers are created, in
     order to carry this information to the RFC 822 recipient.  These
     fields are "X400-Originator:"  and "X400-Recipients:".

          The "X400-Originator:" field is set to the same value as the
     SMTP originator.  In addition, if
     MTS.OtherMessageDeliveryFields.originator-name (MTS.ORName)
     contains MTS.ORName.directory-name then this Directory Name shall
     be represented in an 822.comment.

          Recipient names, taken from each value of
     MTS.OtherMessageDeliveryFields.this-recipient-name and
     MTS.OtherMessageDeliveryFields.other-recipient-names are made
     available to the RFC 822 user by use of the "X400-Recipients:"
     field.  By taking the recipients at the MTS level, disclosure of
     recipients will be dealt with correctly.  However, this conflicts
     with a desire to optimise mail transfer.  There is no problem
     when disclosure of recipients is allowed. Similarly, there is no
     problem if there is only one RFC 822 recipient, as the
     "X400-Recipients" field is only given one address.

          There is a problem if there are multiple RFC 822 recipients,
     and disclosure of recipients is prohibited.  In this case,
     discard the per-recipient information.

     If any MTS.ORName.directory-name is present, it shall be



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     represented in an 822.comment.

          If
     MTS.OtherMessageDeliveryFields.orignally-intended-recipient-name
     is present, then there has been redirection,  or there has been
     distribution list expansion.  Distribution list expansion is a
     per-message option, and the information associated with this is
     represented by the "DL-Expansion-History:" field described in
     Section 5.3.6.  Other information is represented in an
     822.comment associated with
     MTS.OtherMessageDeliveryFields.this-recipient-name, The message
     may be delivered to different RFC 822 recipients, and so several
     addresses in the "X400-Recipients:" field may have such comments.
     The non-commented recipient is the RFC 822 recipient. The EBNF of
     the comment is defined by redirect-comment.

             redirect-comment  = redirect-first *( redirect-subsequent )

             redirect-first = "Originally To:"  mailbox  "Redirected on"
                      date-time "To:"  redirection-reason

             redirect-subsequent = mailbox  "Redirected Again on"
                      date-time "To:"  redirection-reason

             redirection-history-item = "intended recipient" mailbox
                      "redirected to"  redirection-reason
                      "on" date-time


             redirection-reason =
                      "Recipient Assigned Alternate Recipient"
                      / "Originator Requested Alternate Recipient"
                      / "Recipient MD Assigned Alternate Recipient"
                      / "Directory Look Up"
                      / "Alias"

     It is derived from
     MTA.PerRecipientMessageTransferFields.extension.redirection-history.
     The values are taken from the X.400(92) Implementor's guide
     (Version 13, July 1995).   The first three values are in
     X.400(88).   The fourth value is in X.400(92), but has the name
     "recipient-directory-substitution-alternate-recipient". An
     example of this with two redirects is:




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     X400-Recipients: postmaster@widget.com (Originally To:
               sales-manager@sales.widget.com
           Redirected on Thu, 30 May 91 14:39:40 +0100
               To: Originator Requested Alternate Recipient
               postmaster@sales.widget.com
           Redirected Again on Thu, 30 May 91 14:41:20 +0100
               To: Recipient MD Assigned Alternate Recipient)



          In addition the following per-recipient services from
     MTS.OtherMessageDeliveryFields.extensions are represented in
     comments if they are used.  None of these services can be
     provided on RFC 822 networks, and so in general these will be
     informative strings associated with other MTS recipients. In some
     cases, string values are defined.  For the remainder, the string
     value shall be chosen by the implementor.   If the parameter has
     a default value, then no comment shall be inserted when the
     parameter has that default value.

     requested-delivery-method

     physical-forwarding-prohibited
          "(Physical Forwarding Prohibited)".

     physical-forwarding-address-request
          "(Physical Forwarding Address Requested)".

     physical-delivery-modes

     registered-mail-type

     recipient-number-for-advice

     physical-rendition-attributes

     physical-delivery-report-request
          "(Physical Delivery Report Requested)".

     proof-of-delivery-request
          "(Proof of Delivery Requested)".





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     4.6.2.3.  Delivery Report Generation

     If SMTP is used, the behaviour is specified in Appendix A.  In
     other cases, if
     MTA.PerRecipientMessageTransferFields.per-recipient-indicators
     requires a positive delivery notification, this shall be
     generated by the gateway.  Supplementary Information shall be set
     to indicate that the report is gateway generated.  This
     information shall include the name of the gateway generating the
     report.

     4.6.3.  Message IDs (MTS)

     A mapping from 822.msg-id to MTS.MTSIdentifier is defined.  The
     reverse mapping is not needed, as MTS.MTSIdentifier is always
     mapped onto new RFC 822 fields.  The value of
     MTS.MTSIdentifier.local-part will facilitate correlation of
     gateway errors.

          To map from 822.msg-id, apply the standard mapping to
     822.msg-id, in order to generate an MTS.ORAddress.  The Country,
     ADMD, and PRMD components of this are used to generate
     MTS.MTSIdentifier.global-domain-identifier.
     MTS.MTSIdentifier.local-identifier is set to the 822.msg-id,
     including the braces "<" and ">".   If this string is longer than
     MTS.ub-local-id-length (32), then it is truncated to this length.

          The reverse mapping is not used in this specification.  It
     would be applicable where MTS.MTSIdentifier.local-identifier is
     of syntax 822.msg-id, and it algorithmically identifies
     MTS.MTSIdentifier.

     4.7.  IPMS Mappings

     All RFC 822 addresses are assumed to use the 822.mailbox syntax.
     This includes all 822.comments associated with the lexical tokens
     of the 822.mailbox.  In the IPMS OR Names are encoded as
     MTS.ORName.  This is used within the  IPMS.ORDescriptor,
     IPMS.RecipientSpecifier, and IPMS.IPMIdentifier.  An asymmetrical
     mapping is defined between these components.

     4.7.1.  RFC 822 -> X.400

     To derive IPMS.ORDescriptor from an RFC 822 address.



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     1.   Take the address, and extract an EBNF.822-address.  Any
          source routing shall be removed.  This can be derived
          trivially from either the 822.addr-spec or 822.route-addr
          syntax.  This is mapped to MTS.ORName as described above,
          and used as IMPS.ORDescriptor.formal-name.

     2.   A string shall be built consisting of (if present):

     -         The 822.phrase component if the 822.address is an
               822.phrase 822.route-addr construct.

     -         Any 822.comments, in order, retaining the parentheses.

          This string is then encoded into T.61 using a human oriented
          mapping (as described in Section 3.5).  If the string is not
          null, it is assigned to IPMS.ORDescriptor.free-form-name.

     3.   IPMS.ORDescriptor.telephone-number is omitted.

     If IPMS.ORDescriptor is being used in IPMS.RecipientSpecifier,
     IPMS.RecipientSpecifier.reply-request and
     IPMS.RecipientSpecifier.notification-requests are set to default
     values (false and none).

          If the 822.group construct is present, any included
     822.mailbox is encoded as above to generate a separate
     IPMS.ORDescriptor.  The 822.group is  mapped to T.61 (as
     described in Section 3.5), and a IPMS.ORDescriptor with only an
     free-form-name component built from it.

     4.7.2.  X.400 -> RFC 822

     Mapping from IPMS.ORDescriptor to RFC 822 address.  In the basic
     case, where IPMS.ORDescriptor.formal-name is present, proceed as
     follows.

     1.   Encode IPMS.ORDescriptor.formal-name (MTS.ORName) as
          EBNF.822-address.

     2a.  If IPMS.ORDescriptor.free-form-name is present, convert it
          to ASCII or T.61 (Section 3.5), and use this as the
          822.phrase component of 822.mailbox using the 822.phrase
          822.route-addr construct.




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     2b.  If IPMS.ORDescriptor.free-form-name is absent.  If
          EBNF.822-address is parsed as 822.addr-spec use this as the
          encoding of 822.mailbox.  If EBNF.822-address is parsed as
          822.route 822.addr-spec, then an 822.phrase taken from
          822.local-part is added.

     3    If IPMS.ORDescriptor.telephone-number is present, this is
          placed in an 822.comment, with the string "Tel ".  The
          normal international form of number is used.  For example:

                  (Tel +44-181-333-7777)


     4.   If IPMS.ORDescriptor.formal-name.directory-name is present,
          then a text representation is placed in a trailing
          822.comment.

     5.   If IPMS.RecipientSpecifier.report-request has any non-
          default values, then an 822.comment "(Receipt Notification
          Requested)", and/or "(Non Receipt Notification Requested)",
          and/or "(IPM Return Requested)" may be appended to the
          address. "(Receipt Notification Requested)" may be used to
          infer "(Non Receipt Notification Requested)".  The effort of
          correlating P1 and P2 information is too great to justify
          the gateway sending Receipt Notifications.

          In RFC 1327, inclusion of these comments was mandatory.
          Experience has shown that the clutter and confusion caused
          to RFC 822 users does not justify the information conveyed.
          Implementors are recommended to not include these comments.
          Unless an application is found where retention of these
          comments is desirable, they will be dropped from the next
          version.

     6.   If IPMS.RecipientSpecifier.reply-request is True, an
          822.comment "(Reply requested)"  is appended to the address.

     If IPMS.ORDescriptor.formal-name is absent,
     IPMS.ORDescriptor.free-form-name is converted to ASCII (see
     section 3.5), and used as 822.phrase within the RFC 822 822.group
     syntax.  For example:

             Free Form Name ":" ";"




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     Steps 3-6 are then followed.

     4.7.3.  IP Message IDs

     There is a need to map both ways between 822.msg-id and
     IPMS.IPMIdentifier.  This allows for X.400 Receipt Notifications,
     Replies, and Cross References to reference an RFC 822 Message ID,
     which is preferable to a gateway generated ID.  A reversible and
     symmetrical mapping is defined.  This provides fully reversible
     mappings when messages pass multiple times across the X.400/RFC
     822 boundary.

          An important issue with messages identifiers is mapping to
     the exact form, as many systems use these ids as uninterpreted
     keys.  The use of table driven mappings is not always
     symmetrical, particularly in the light of alternative domain
     names, and alternative management domains.  For this reason, a
     purely algorithmic mapping is used.  A mapping which is simpler
     than that for addresses can be used for two reasons:

     -    There is no major requirement to make message IDs "natural"

     -    There is no issue about being able to reply to message IDs.
          (For addresses, creating a return path which works is more
          important than being symmetrical).

     The mapping works by defining a way in which message IDs
     generated on one side of the gateway can be represented on the
     other side in a systematic manner.  The mapping is defined so
     that the possibility of clashes is low enough to be treated as
     impossible.

     4.7.3.1.  822.msg-id represented in X.400

     IPMS.IPMIdentifier.user is omitted.  The
     IPMS.IPMIdentifier.user-relative-identifier is set to a printable
     string encoding of the 822.msg-id with the angle braces ("<" and
     ">") removed.  The upper bound on this component is 64.  The
     options for handling this are discussed in Section 5.1.3.

     4.7.3.2.  IPMS.IPMIdentifier represented in RFC 822

     The 822.domain of 822.msg-id is set to the value "MHS". The
     822.local-part of 822.msg-id is constructed by building a string



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     of syntax EBNF.id-loc from IPMS.IPMIdentifier.

             id-loc ::= [ printablestring ] "*"  [ std-or-address ]

     EBNF.printablestring is the
     IPMS.IPMIdentifier.user-relative-identifier, and EBNF.std-or-
     address being an encoding of the IPMS.IPMIdentifier.user derived
     according to this specification.  822.local-part is derived from
     EBNF.id-loc, if necessary using the 822.quoted-string encoding.
     For example:

     <"147*/S=Dietrich/O=Siemens/ADMD=DBP/C=DE/"@MHS>


     4.7.3.3.  822.msg-id -> IPMS.IPMIdentifier

     If the 822.local-part can be parsed as:

             [ printablestring ] "*"  [ std-or-address ]

     and the 822.domain is "MHS", then this ID was X.400 generated.
     If EBNF.printablestring is present, the value is assigned to
     IPMS.IPMIdentifier.user-relative-identifier.  If
     EBNF.std-or-address is present, the OR Address components derived
     from it are used to set IPMS.IPMIdentifier.user.

          Otherwise, this is an RFC 822 generated ID.  In this case,
     set IPMS.IPMIdentifier.user-relative-identifier to a printable
     string encoding of the 822.msg-id without the angle braces and
     omit IPMS.IPMID.user.

     4.7.3.4.  IPMS.IPMIdentifier -> 822.msg-id

          If IPMS.IPMIdentifier.user is absent, and
     IPMS.IPMIdentifier.user-relative-identifier mapped to ASCII and
     angle braces added parses as 822.msg-id, then this is an RFC 822
     generated ID.

          Otherwise, the ID is X.400 generated.  Use the
     IPMS.IPMIdentifier.user to generate an EBNF.std-or-address form
     string.  Build the 822.local-part of the 822.msg-id with the
     syntax:

             [ printablestring ] "*"  [ std-or-address ]



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     The printablestring is taken from
     IPMS.IPMIdentifier.user-relative-identifier.  Use
     822.quoted-string if necessary.  The 822.msg-id is generated with
     this 822.local-part, and "MHS" as the 822.domain.

     4.7.3.5.  Phrase form

     In "In-Reply-To:" and "References:", the encoding 822.phrase may
     be used as an alternative to 822.msg-id.  To map from 822.phrase
     to IPMS.IPMIdentifier, assign
     IPMS.IPMIdentifier.user-relative-identifier to the phrase.  When
     mapping from IPMS.IPMIdentifier for "In-Reply-To:" and
     "References:", if IPMS.IPMIdentifier.user is absent and
     IPMS.IPMIdentifier.user-relative-identifier does not parse as
     822.msg-id, generate an 822.phrase rather than adding the domain
     MHS.

     4.7.3.6.  RFC 987 backwards compatibility

     The mapping defined here is different to that used in RFC 987, as
     the RFC 987 mapping lead to changed message IDs in many cases.
     Fixing the problems is preferable to retaining backwards
     compatibility.  An implementation of this standard may recognise
     message IDs generated by RFC 987.  This is not recommended.

          RFC 987 generated encodings may be recognised as follows.
     When mapping from X.400 to RFC 822, if the
     IPMS.IPMIdentifier.user-relative-identifier is "RFC-822" the id
     is RFC 987 generated. When mapping from RFC 822 to X.400, if the
     822.domain is not "MHS", and the 822.local-part can be parsed as

             [ printablestring ] "*"  [ std-or-address ]

     then it is RFC 987 generated.  In each of these cases, it is
     recommended to follow the RFC 987 rules.












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     Chapter 5 - Detailed Mappings


     This chapter specifies  detailed mappings for the functions
     outlined in Chapters 1 and 2.  It makes extensive use of the
     notations and mappings defined in Chapters 3 and 4.


     5.1.  RFC 822 -> X.400: Detailed Mappings

     The mapping of RFC 822/MIME messages to X.400 InterPersonal
     Messages is described in Sections 5.1.1 to 5.1.7.   Mapping of
     NOTARY format delivery status notifications, which are all
     messages of type multipart/report and subtype
     delivery-status-notifications to X.400 delivery reports is
     covered in Section 5.1.8.


     5.1.1.  Basic Approach

     A single IP Message is generated from an RFC 822 message.  The
     RFC 822 headers are used to generate the IPMS.Heading.

          Some RFC 822 fields cannot be mapped onto a standard IPM
     Heading field, and so an extended field is defined in Section
     5.1.2.  This is then used for fields which cannot be mapped onto
     existing services.

          The message is submitted to the MTS, and the services
     required can be defined by specifying
     MTS.MessageSubmissionEnvelope.  A few parameters of the MTA
     Abstract service are also specified, which are not in principle
     available to the MTS User.  Use of these services allows RFC 822
     MTA level parameters to be carried in the analogous X.400 service
     elements.  The advantages of this mapping far outweigh the
     layering violation.

     5.1.2.  X.400 Extension Field

     An IPMS Extension is defined:







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     rfc-822-field HEADING-EXTENSION
             VALUE RFC822FieldList
             ::= id-rfc-822-field-list


     RFC822FieldList ::= SEQUENCE OF RFC822Field

     RFC822Field ::= IA5String


     The Object Identifier id-rfc-822-field-list is defined in
     Appendix D.

          To encode any RFC 822 Header using this extension, an
     RFC822Field element is built using the 822.field omitting the
     trailing CRLF (e.g., "Fruit-Of-The-Day: Kiwi Fruit"). All fields
     shall be unfolded.  There shall be no space before the ":".  The
     reverse mapping builds the RFC 822 field in a straightforward
     manner.  This RFC822Field is appended to the RFC822FieldList,
     which is added to the IPM Heading as an extension field.

     5.1.3.  Generating the IPM

     The IPM (IPMS Service Request) is generated according to the
     rules of this section. The IPMS.IPM.body is generated from the
     RFC 822 message body in the manner described in Section 5.1.5.

          If no specific 1988 features are used, the IPM generated is
     encoded as content type 2.  Otherwise, it is encoded as content
     type 22.  The latter will always be the case if extension heading
     fields are generated.

          When generating the IPM, the issue of upper bounds are
     handled as follows. Truncate fields to the upper bounds specified
     in X.400.  This will prevent problems with UAs which enforce
     upper bounds, but will sometimes discard useful information.
     This approach will cause more problems for some fields than
     others (e.g., truncating an OR Address component that would be
     used to route a reply would be a more severe problem than
     truncating a Free Form Name).  If the Free Form name is
     truncated, it shall be done so that it does not break RFC 822
     comments and RFC 1522 encoding.




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     Note:This approach removes a choice of options given in RFC 1327,
          based on operational experience.

          The rest of this section concerns IPMS.IPM.heading
     (IPMS.Heading).  The only mandatory component of IPMS.Heading is
     the IPMS.Heading.this-IPM (IPMS.IPMIdentifier).  A default is
     generated by the gateway.  With the exception of "Received:", the
     values of multiple fields are merged (e.g., If there are two
     "To:" fields, then the mailboxes of both are merged to generate a
     single list which is used in the IPMS.Heading.primary-recipients.
     Information shall be generated from the standard RFC 822 Headers
     as follows:

     Date:
          Ignore (Handled at MTS level)

     Received:
          Ignore (Handled at MTA level)

     Message-Id:
          Mapped to IPMS.Heading.this-IPM.  For these, and all other
          fields containing 822.msg-id the mappings of Chapter 4 are
          used for each 822.msg-id.

     From:
          If Sender: is present, this is mapped to
          IPMS.Heading.authorizing-users.  If not, it is mapped to
          IPMS.Heading.originator.  For this, and other components
          containing addresses, the mappings of Chapter 4 are used for
          each address.

     Sender:
          Mapped to IPMS.Heading.originator.  Because X.400 does not
          have the same From/Sender distinction as RFC 822, this
          mapping is not always natural and may lead to unexpected
          results in some cases.

     Reply-To:
          Mapped to IPMS.Heading.reply-recipients.

     To:  Mapped to IPMS.Heading.primary-recipients

     Cc:  Mapped to IPMS.Heading.copy-recipients.




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     Bcc: Mapped to IPMS.Heading.blind-copy-recipients if there is at
          least one BCC: recipient.  If there are no recipients in
          this field, it shall either be mapped to a zero length
          sequence or mapped to a single recipient that has a free
          from name "BCC" and no other addressing information.  This
          alternate treatment is allowed because some X.400 systems
          cannot handle a zero lenght sequence of addresses.

     In-Reply-To:
          If there is one value, it is mapped to
          IPMS.Heading.replied-to-IPM, using the 822.phrase or
          822.msg-id mapping as appropriate.  If there are multiple
          values, this cannot be done as the X.400 heading is single
          valued. In this case no IPMS.Heading.replied-to-IPM is
          generated and the values are mapped to
          IPMS.Heading.related-IPMs, along with any values from a
          "References:" field.

     References:
          Mapped to IPMS.Heading.related-IPMs.

     Keywords:
          Mapped onto a heading extension.

     Subject:
          Mapped to IPMS.Heading.subject.  The field-body uses the
          human oriented mapping referenced in Section 3.3.4.

     Comments:
          Mapped onto a heading extension.

          This is a change from 1327, which specified to generate an
          IPMS.BodyPart of type IPMS.IA5TextBodyPart with
          IPMS.IA5TextBodyPart.parameters.repertoire set to the
          default (ia5), containing the value of the fields, preceded
          by the string "Comments: " and that this body part shall
          precede the other one. Experience has shown that this
          complexity is not justified.  This text is retained to
          facilitate backwards compatibility.

     Encrypted:
          Mapped onto a heading extension.

     Resent-*



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          Mapped onto a heading extension.

          Note that it would be possible to use a ForwardedIPMessage
          for these fields, but the semantics are (arguably) slightly
          different, and it is probably not worth the effort.

     Content-Language:
          This field is defined in RFC 1766 [7].  Map the first two
          characters of each value given onto the IPM Languages
          extension. If any comments or values longer than two
          characters occur, a header extension shall also be
          generated.

     Other Fields
          In particular X-* fields, and "illegal" fields in common
          usage (e.g., "Fruit-of-the-day:") are mapped onto a heading
          extension, unless covered by another section or appendix of
          this specification.  The same treatment is applied to RFC
          822 fields where the content of the field does not conform
          to RFC 822 (e.g., a Date: field with unparseable syntax).

     The mapping of the following headings is defined in RFC1494bis.

     MIME-Version: 5
     Content-Transfer-Encoding:
     Content-Type
     Content-ID
     Content-Description

     5.1.4.  Generating the IPM Body

     Generation of the IPM Body is defined in RFC1494bis.

     5.1.5.  Mappings to the MTS Abstract Service

     The MTS.MessageSubmissionEnvelope comprises
     MTS.PerMessageSubmissionFields, and
     MTS.PerRecipientMessageSubmissionFields.  The mandatory
     parameters are defaulted as follows.

     MTS.PerMessageSubmissionFields.originator-name
          This is always generated from SMTP, as defined in Chapter 4.

     MTS.PerMessageSubmissionFields.content-type



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          Set to the value implied by the encoding of the IPM (2 or
          22).

     MTS.PerRecipientMessageSubmissionFields.recipient-name
          These will always be supplied from SMTP, as defined in
          Chapter 4.

     Optional components are omitted, and default components
     defaulted.  This means that disclosure of recipients is
     prohibited and conversion is allowed.  There are two exceptions
     to the defaulting. For
     MTS.PerMessageSubmissionFields.per-message-indicators, the
     following settings are made:

     -    Alternate recipient is allowed, as it seems desirable to
          maximise the opportunity for (reliable) delivery.

     If SMTP is used, Appendix A shall be followed in setting these
     parameters.

          The trace is set to indicate conversion (described below)
     and the encoded information types in the trace is derived from
     the message generated by the gateway, and shall reflect all body
     parts (including those in enclosed messages).  In addition it
     shall include the Encoded Information Type "eit-mixer", which is
     defined in Appendix D.   The presence of the EIT will indicate to
     the X.400 recipient that a MIXER conversion has occurred.
     MTS.PerMessageSubmissionFields.original-encoded-information-types
     will include all of the values used in the trace, unless
     specified otherwise in RFC1494bis.

          This type of conversion will prevent the normal loop
     detection from working in certain circumstances, and introduces
     the possiblity of gateway loops.  MIXER gateways shall therefore
     count the number of MIXER conversions made.  If this count
     exceeds five in one direction, the message shall be treated as if
     a loop has been detected.

          The MTS.PerMessageSubmissionFields.content-correlator is
     encoded as IA5String, and contains the Subject:, Message-ID:,
     Date:,  and To: fields (if present) in this order.  This
     includes the strings "Subject:", "Date:", "To:", "Message-ID:",
     and appropriate folding to make the field appear readable.  This
     shall be truncated to MTS.ub-content-correlator-length (512)



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     characters.  In addition, if there is a "Subject:" field, the
     MTS.PerMessageSubmissionFields.content-identifier, is set to a
     printable string representation of the contents of it.   If the
     length of this string is greater than MTS.ub-content-id-length
     (16), it shall be truncated to 13 characters and the string "..."
     appended. Both are used, due to the much larger upper bound of
     the content correlator, and that the content id is available in
     X.400(1984).

     5.1.6.  Mappings to the MTA Abstract Service

     There is a need to map directly onto some aspects of the MTA
     Abstract service, for the following reasons:

     -    So the  MTS Message Identifier can be generated from the RFC
          822 Message-ID:.

     -    So that the submission date can be generated from the
          822.Date.

     -    To prevent loss of trace information

     -    To prevent RFC 822/X.400 looping caused by distribution
          lists or redirects

     The following mappings are defined.

     Message-Id:
          If this is present and no Resent: fields are present, the
          MTA.PerMessageTransferFields.message-identifier may be
          generated from it, using the mappings described in
          Chapter 4.

          This mapping arguably generates messages which do not
          conform to US GOSIP (1984 version only), which states:

          6.7.e MPDU Identifier Validation

          (1) Validation of the GlobalDomainIdentifier component of
          the MPDU Identifier is performed on reception of a message
          (i.e. the result of a TRANSFER.Indication).

          (2) The country name should be known to the validating
          domain, and depending on the country name, validation of the



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          ADMD name may also be possible.

          (3) Additional validation of the GlobalDomainIdentifier is
          performed against the corresponding first entry in the
          TraceInformation. If inconsistencies are found during the
          comparison, a non-delivery notice with the above defined
          reason and diagnostic code is generated.

          (4) A request will be generated to the CCITT for a more
          meaningful diagnostic code (such as
          "InconsistentMPUTIdentifier").

          This applies to ADMDs only, and is specified in the 1984
     version and not the 1988 version. Conformance depends on the
     interpretation of "inconsistency".   The specification makes the
     most sensible choice, and so is not being changed in the update
     from RFC 1327.

     Date: (and Resent-Date:)
          If one or more Resent-Date: fields is present, the most
          recent Resent-Date: field shall be used instead of the Date:
          field in the following description.

          The Date: field is used to set the first component of
          MTA.PerMessageTransferFields.trace-information
          (MTA.TraceInformationElement).  The SMTP originator is
          mapped into an MTS.ORAddress, and used to derive
          MTA.TraceInformationElement.global-domain-identifier.  The
          optional components of
          MTA.TraceInformationElement.domain-supplied-information are
          omitted, and the mandatory components are set as follows:

            MTA.DomainSuppliedInformation.arrival-time
               This is set to the date derived from Date:

            MTA.DomainSuppliedInformation.routing-action
               Set to relayed.

          The first element of
          MTA.PerMessageTransferFields.internal-trace-information is
          generated in an analogous manner, although this can be
          dropped later in certain circumstances (see the procedures
          for "Received:").  The
          MTA.InternalTraceInformationElement.mta-name is derived from



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          the 822.domain in the 822 MTS Originator address.

     Received:
          All RFC 822 trace is used to derive
          MTA.PerMessageTransferFields.trace-information and
          MTA.PerMessageTransferFields.internal-trace-information.
          Processing of Received: lines  follows processing of Date:,
          and is done from the bottom to the top of the RFC 822 header
          (i.e., in chronological order).  When other trace elements
          (in particular X400-Received:)  are processed the relative
          ordering (top to bottom of the header) shall be retained
          correctly.

          The initial element of
          MTA.PerMessageTransferFields.trace-information shall be
          generated from Date: as described above, unless the message
          has previously been in X.400, when it will be derived from
          the X.400 trace information.

          For each  Received: field, the following processing shall be
          done.  If the "by"  part of the received is present and
          there is an available MCGAM which can map this domain, use
          it to derive an MTS.GlobalDomainIdentifier.  Otherwise
          MTS.GlobalDomainIdentifier is set from local information.
          If this is different from the one in the last element of
          MTA.PerMessageTransferFields.trace-information
          (MTA.TraceInformationElement.global-domain-identifier)
          create a new MTA.TraceInformationElement, and optionally
          remove
          MTA.PerMessageTransferFields.internal-trace-information.
          Requirements on trace stripping are discussed below.

          Then add a new element (MTA.InternalTraceInformationElement)
          to MTA.PerMessageTransferFields.internal-trace-information,
          creating this if needed.  This shall be done, even if
          inter-MD trace is created.  The
          MTA.InternalTraceInformationElement.global-domain-identifier
          is set to the value derived.  The
          MTA.InternalTraceInformationElement.mta-supplied-information
          (MTA.MTASuppliedInformation) is set as follows:

            MTA.MTASuppliedInformation.arrival-time
               Derived from the date of the Received: line




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            MTA.MTASuppliedInformation.routing-action
               Set to relayed

          The MTA.InternalTraceInformationElement.mta-name is taken
          from the "by" component of the "Received:" field, truncated
          to MTS.ub-mta-name-length (32).  For example:


             Received: from computer-science.nottingham.ac.uk by
                vs6.Cs.Ucl.AC.UK via Janet with NIFTP  id aa03794;
                28 Mar 89 16:38 GMT

     Generates the string

             vs6.Cs.Ucl.AC.UK


     The gateway shall add in a single element of trace information,
     reflecting the gateway's local information and the time of
     conversion.  The
     MTA.InternalTraceInformationElement.mta-supplied-information
     (MTA.MTASuppliedInformation) is set as follows:

     MTA.DomainSuppliedInformation.arrival-time
          Set to the time of conversion

     MTA.DomainSuppliedInformation.routing-action
          Set to relayed

     MTA.AdditionalAcctions.converted-encoded-information-types
          Set to correct set of EITs for the message that is generated
          by the gateway.   This trace element will thus reflect
          gateway operation as a conversion.

     This trace generation will often lead to generation of
     substantial amounts of trace information, which does not reflect
     X.400 transfers.  Stripping of some of this trace may be
     necessary in some operational environments.   This stripping
     shall be considered a function of the associated X.400 MTA, and
     not of the MIXER gateway.

     5.1.7.  Mapping New Fields

     This specification defines a number of new fields for Reports,



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     Notifications and IP Messages. A gateway conforming to this
     specification shall  map all of these fields to X.400, except as
     defined below.

          The mapping of two  extended fields is particularly
     important, in order to prevent looping.  "DL-Expansion-History:"
     is mapped to
     MTA.PerMessageTransferFields.extensions.dl-expansion-history
     X400-Received: shall be mapped to
     MTA.PerMessageTransferFields.trace-information and
     MTA.PerMessageTransferFields.internal-trace-information.  In
     cases where X400-Received: is present, the usual mapping of Date:
     to generate the first element of trace shall not be done.   This
     is because the message has come from X.400, and so the first
     element of trace can be taken from the first X400-Received:.

          The following fields shall not be mapped, and shall be
     discarded:

     -    Discarded-X400-MTS-Extensions:

     -    Message-Type:

     -    Discarded-X400-IPMS-Extensions:

     -    X400-Content-Type:

     -    X400-Originator:

     -    X400-Recipients:

     -    X400-MTS-Identifier:  Mapping this field would be useful in
          some circumstances, but very dangerous in others (e.g.,
          following an internet list expansion).  Therefore it is not
          mapped.

     5.1.8.  Mapping Delivery Status Notifications to X.400


     5.1.8.1.  Basic Model

     Internet Mail delivery status notifications (DSN) are mapped to
     X.400 delivery reports.   With message mapping, information
     without a mapping is carried by an IPM Extension.   This cannot



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     be done for delivery reports.   Two mechanisms are used for
     information where there is not a direct mapping.

          The first mechanism is to define extensions, which allow all
     of the DSN information to be carried in the delivery report.
     This is not completely satisfactory for two reasons:

     1.   User defined extensions are supported by the ISO version of
          the standard, but not the CCITT one.  Therefore,
          implementation support for these extensions will not be
          universal.

     2    X.400 User Agent implementations will not in general
          recognise these extensions.   Therefore, although the
          information will be present, it will often not be available
          to the user.    This may be very problematic, as this
          information may be critical to diagnosing the reason for a
          failure.

          Therefore a second mechanism is defined.  This shall always
     be used when the DSN contains non-delivery information, and may
     be used in other cases.  This mechanism is to map the whole DSN
     (as if it were an ordinary multipart) into the return of content.
     This will make the DSN information available as a text body part
     in the outer message, with the real returned content as an
     enclosed message.  This mechanism will ensure that information is
     not lost at the gateway.

     5.1.8.2.  DSN Extensions

     Two X.400 MTS extensions are defined as follows:

     dsn-header-list EXTENSION
        RFC822FieldList
        ::= id-dsn-header-list

     dsn-field-list EXTENSION
        RFC822FieldList
        ::= id-dsn-field-list

     The Object Identifiers id-dsn-header-list and id-dsn-field-list
     are defined in Appendix D.  Theses extensions are used in the
     same way as the IPM extension rfc-822-field, described in Section
     5.1.2.   These extensions may only be used with ISO-10021, and



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     not X.400 (which does not allow user extensions at the MTS
     level).

     5.1.8.3.  DSN to Delivery Report Mapping

     Some DSNs are mapped to Delivery Reports and some to IPMs,
     according to the value of the action field.   The mapping to an
     IPM is exactly as for a normal IPM mapping.   The choice of IPM
     and Delivery report is made for each reported recipient.   If
     this choice is different for different reported recipients both a
     Delivery Report and an IPM shall be generated.

          Reports are not be submitted in the X.400 model, and so the
     report submission is considered in terms of the MTA Abstract
     Service.  An MTA.Report is constructed. The
     MTA.ReportTransferEnvelope.report-identifier is generated from
     the Message-Id of the DSN (if present) and otherwise generated as
     the MTA would generate one for a submitted message.

          The DSN has an RFC 822 header.  Trace is mapped in the same
     manner as for a message to
     MTA.ReportTransferEnvelope.trace-information.  All other headers
     are used to create a dsn-header-list extension, which is added to
     MTA.PerReportTransferFields.extensions.

          The DSN will have a single SMTP recipient.   This is mapped
     to the MTA.ReportTransferEnvelope.report-destination-name.

          The DSN is then treated as a normal MIME message, and an
     X.400 IPM is generated.   This IPM is used as
     MTA.PerReportTransferFields.returned-content, and its type is
     used to set MTA.PerReportTransferFields.content-type.  The DSN
     body part is mapped as if it was IA5 text/plain.

          The mandatory MTA.PerReportTransferFields.subject-identifier
     shall be generated from the DSN.per-message-field
     original-envelope-id, if this starts with the string
     "X400-MTS-Identifier: ", and derived from the rest of the field,
     which is encoded as EBNF.mts-msg-id.  In other cases, this field
     shall be generated by the MIXER Gateway.

          All other mappings are made from the DSN body part. A dsn-
     field-list extension is created and added to
     MTA.ReportTransferFields.extensions.  This is referred to as the



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     per report extension list.  The DSN.per-message-fields are mapped
     as follows:

     original-envelope-id-field
     reporting-mta-field
     dsn-gateway-field
     received-from-mta-field
     arrival-date-field
     extension-field
     other


          All of these fields are added to the per report extension
          list.  Currently there are no other mappings defined.

     Each reported recipient is considered in turn, and a
     MTA.PerRecipientReportTransferFields created for each.  The
     parameters of this are defaulted as follows:

     originally-specified-recipient-number
          In general, these are not available, and so are assigned
          incrementally.

     last-trace-information
          The arrival-time is generated from DSN.arrival-date if
          present, and if not from the Date: of the DSN.  This is a
          strucutred field, and the Report element contains the key
          information on the recipient.  For a DeliveryReport, the
          type-ofMTS-user is defaulted to public and the
          message-deliery-time is set to the same as the arrival-time.
          For a NonDeliveryReport, the code mappings are define in
          Section 5.1.8.4.

          A dsn-field-list extension is created  and added to
     MTA.PerRecipientTransferFields.extensions.  This is referred to
     as the per recipient extension list.  The
     DSN.per-recipient-fields are mapped as follows

     original-recipient-field
          Mapped to
          MTA.PerRecipientReportTransferFields.originally-intended-recipient-name.

     final-recipient-field
          Mapped to



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          MTA.PerRecipientReportTransferFields.actual-recipient-name.

     action-field
          If this is set to "failed", a non-delivery report is
          generated.  If this is set to "delivered" a delivery report
          is generated.   Bit one or two of
          MTA.PerRecipientTransferFields.per-recipient-indicators is
          set accordingly.  This also controls the encoding of
          MTA.PerRecipientTransferFields.last-trace-information, and
          the selection of the report type.

          For other values of the action-field ("delayed", "relayed",
          "expanded"), an IPM is generated.   This enables the status
          information to be communicated to the X.400 user, without
          the confusion of multiple delivery reports.

     status-field
          This is added to the per report extension list.  For non-
          delivery, it is also used to generate the reason and
          diagnostic codes contained within
          MTA.PerRecipientReportTransferFields.last-trace.  The
          mappings are defined below.

     remote-mta-field

     diagnostic-code-field

     last-attempt-date-field

     will-retry-until-field

     extension-field

     other
          All of these fields are added to the per recipient extension
          list.

     5.1.8.4.  Status Value Mappings

     Status values are mapped to X.400 reason and diagnostic codes as
     follows.

          If a status value is found that is not in this table, the
     gateway may use the same mapping as for "X.n.0" (1/None or



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RFC 1327bis
MIXER                                                DRAFT Version 2.6


     0/None), or it may map to another, configurable code.
     Implementors are requested to forward new codes to the mixer list
     for inclusion in future versions of this standard.  So for
     instance. "5.2.37", currently undefined, would map onto the same
     as "5.2.0", namely 1/None.

     DSN code  Meaning                               X400 code Meaning

     X.0.0     Other status                          1/None

     X.1.0     Other Address Status                  1/None
     X.1.1     Bad mailbox address                   1/0     Unrecognized
     X.1.2     Bad system address                    1/0     Unrecognized
     X.1.3     Bad mailbox address syntax            1/0     Unrecognized
     X.1.4     Mailbox address ambiguous             1/1
     X.1.5     Only used for positive reports, not applicable
     X.1.6     Destination mailbox has moved         1/43    New address unknown
     X.1.7     Bad sender's mailbox address syntax   1/11    Invalid arguments
     X.1.8     Bad sender's system address        1/11    Invalid arguments



     X.2.0     Other or undefined mailbox status     1/None
     X.2.1     Mailbox disabled, not accepting       1/4     Recipient unavailable
     X.2.2     Mailbox full                          1/4
     X.2.3     Message length exceeds admin limit.   1/7     Content too long
     X.2.4     Mailing list expansion problem        1/30    DL expansion failure

     X.3.0     Other or undefined system status      0/None
     X.3.1     System full                           1/2     MTS congestion
     X.3.2     System not accepting network messages 1/2     MTS congestion
     X.3.3     System not capable of selected feat   1/18    Unsupp. crit. func
     X.3.4     Message too big for system            1/7
     X.3.5     System incorrectly configured      1/None













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     X.4.0     Other or undefined network or routing 0/None
     X.4.1     No answer from host                   0/None
     X.4.2     Bad connection                        0/None
     X.4.3     Routing server failure                6/None  Directory op unsucc.
     X.4.4.    Unable to route                       0/None
     X.4.5     Network congestion                    1/2     MTS congest.
     X.4.6     Routing loop detected                 1/3
     X.4.7     Delivery time expired                 1/5

     X.5.0     Other or undefined protocol status    1/None

     X.5.1     Invalid command                       1/14    Protocol viol.
     X.5.2     Syntax error                          1/14
     X.5.3     Too many recipients                   1/16
     X.5.4     Invalid command arguments             1/14
     X.5.5     Wrong protocol version                1/18    Unsupp.crit.func


     X.6.0     Other or undefined media error        2/None  Conv. not perf
     X.6.1     Media not supported                   1/6     EIT unsupp.
     X.6.2     Conversion required and prohibited    1/9
     X.6.3     Conversion required but not supported 2/8
     X.6.4     Conversion with loss performed        POSITIVE only
     X.6.5     Conversion failed                  2/47     Unable to downgrade

     X.7.0     Other or undefined security status    1/46
     X.7.1     Delivery not authorized, message ref  1/29    No DL submit perm
     X.7.2     Mailing list expansion prohibited     1/28
     X.7.3     Security conversion req but not poss  1/46    Secure mess. error
     X.7.4     Security features not supported       1/46
     X.7.5     Cryptographic failure                 1/46
     X.7.6     Cryptographic algorithm not supported 1/46
     X.7.7     Message integrity failure             1/46


     5.1.8.5.  DSNs that originated in X.400

     The mapping of X.400 delivery reports to DSNs will in general
     provide sufficient information to make a useful reverse mapping.
     Messages will often be mapped multiple times, commonly due to
     forwarding messages and to distribution lists.   Multiple
     mappings for delivery reports will be a good deal less common.
     For this reason, the reverse mapping of the X.400 DSN extensions



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     defined in MIXER is optional.

     5.2.  Return of Contents

     RFC 1327 offered two approaches for return of content, as this
     service is optional in X.400 and expected in RFC 822.   MIXER
     simply requires that a gateway requests the return of content
     service from X.400.

     5.3.  X.400 -> RFC 822: Detailed Mappings

     5.3.1.  Basic Approach

     A single RFC 822 message is generated from the incoming IP
     Message, Report, or IP Notification.   All IPMS.BodyParts are
     mapped onto a single RFC 822 body.  Other services are mapped
     onto RFC 822 header fields.  Where there is no appropriate
     existing field, new fields are defined for IPMS, MTS and MTA
     services.

          The gateway mechanisms will correspond to MTS Delivery.  As
     with submission, there are aspects where the MTA (transfer)
     services are also used. In particular, there is an optimisation
     to allow for multiple SMTP recipients.

     5.3.2.  RFC 822 Settings

     An RFC 822 Message has a number of mandatory fields in the RFC
     822 Header.  Some SMTP services mandate specification of an SMTP
     Originator.  Even in cases where this is optional, it is usually
     desirable to specify a value.  The following defaults are
     defined, which shall be used if the mappings specified do not
     derive a value:

     SMTP Originator
          If this is not generated by the mapping (e.g., for a
          Delivery Report), a value pointing at a gateway
          administrator shall be assigned.

     Date:
          A value will always be generated

     From:
          If this is not generated by the mapping, it is assigned



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          equal to the SMTP Originator.  If this is gateway generated,
          an appropriate 822.phrase shall be added.

     At least one recipient field
          If no recipient fields are generated, a field "To: list:;",
          shall be added.

     This will ensure minimal RFC 822 compliance.  When generating RFC
     822 headers, folding may be used.  It is recommended to do this,
     following the guidelines of RFC 822.

     5.3.3.  Basic Mappings

     5.3.3.1.  Encoded Information Types

     This mapping from MTS.EncodedInformationTypes is needed in
     several disconnected places.  EBNF is defined as follows:

             encoded-info    = 1#encoded-type

             encoded-type    = built-in-eit / object-identifier

             built-in-eit    = "Undefined"         ; undefined (0)
                             / "Telex"             ; tLX (1)
                             / "IA5-Text"          ; iA5Text (2)
                             / "G3-Fax"            ; g3Fax (3)
                             / "TIF0"              ; tIF0 (4)
                             / "Teletex"           ; tTX (5)
                             / "Videotex"          ; videotex (6)
                             / "Voice"             ; voice (7)
                             / "SFD"               ; sFD (8)
                             / "TIF1"              ; tIF1 (9)


     MTS.EncodedInformationTypes is mapped onto EBNF.encoded-info.
     MTS.EncodedInformationTypes.non-basic-parameters is ignored.
     Built in types are mapped onto fixed strings (compatible with
     X.400(1984) and RFC 987), and other types are mapped onto
     EBNF.object-identifier.

     5.3.3.2.  Global Domain Identifier

     The following simple EBNF is used to represent
     MTS.GlobalDomainIdentifier:



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             global-id = std-or-address

     This is encoded using the std-or-address syntax, for the
     attributes within the Global Domain Identifier.

     5.3.4.  Mappings from the IP Message

     Consider that an IPM has to be mapped to RFC 822.  The IPMS.IPM
     comprises an IPMS.IPM.heading and IPMS.IPM.body.   The heading is
     considered first.  Some EBNF for new fields is defined:

             ipms-field = "Supersedes" ":" 1*msg-id
                        / "Expires" ":" date-time
                        / "Reply-By" ":" date-time
                        / "Importance" ":" importance
                        / "Sensitivity" ":" sensitivity
                        / "Autoforwarded" ":" boolean
                        / "Incomplete-Copy" ":"
                        / "Content-Language" ":" 1#language
                        / "Message-Type" ":" message-type
                        / "Discarded-X400-IPMS-Extensions" ":" 1#object-identifier
                        / "Autosubmitted" ":" autosubmitted



             importance      = "low" / "normal" / "high"


             sensitivity     = "Personal" / "Private" /
                                    "Company-Confidential"

             language        = 2*ALPHA [ "(" language-description ")" ]
             language-description = printable-string



             message-type    = "Delivery Report"
                             / "InterPersonal Notification"
                             / "Multiple Part"







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RFC 1327bis
MIXER                                                DRAFT Version 2.6



             autosubmitted   = "not-auto-submitted"
                             / "auto-generated"
                             / "auto-replied"
                             / "auto-forwarded"

     The mappings and actions for the IPMS.Heading are now specified
     for each element.  Addresses and Message Identifiers are mapped
     according to Chapter 4.
      Other mappings are explained, or are straightforward
     (algorithmic).  If a field with addresses contains zero elements,
     it shall be discarded, except for
     IPMS.Heading.blind-copy-recipients, which can be mapped onto BCC:
     (the only RFC 822 field which allows zero recipients).

     IPMS.Heading.this-IPM
          Mapped to "Message-ID:".

     IPMS.Heading.originator
          If IPMS.Heading.authorizing-users is present this is mapped
          to Sender:, if not to "From:".

     IPMS.Heading.authorizing-users
          Mapped to "From:".

     IPMS.Heading.primary-recipients
          Mapped to "To:".

     IPMS.Heading.copy-recipients
          Mapped to "Cc:".

     IPMS.Heading.blind-copy-recipients
          Mapped to "Bcc:".

     IPMS.Heading.replied-to-ipm
          Mapped to "In-Reply-To:".

     IPMS.Heading.obsoleted-IPMs
          Mapped to the extended RFC 822 field "Supersedes:".   The
          replaces the RFC 1327 field "Obsoletes:".   Reverse mapping
          of the RFC 1327 field may be supported.

     IPMS.Heading.related-IPMs
          Mapped to "References:".



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     IPMS.Heading.subject
          Mapped to "Subject:".  The contents are converted to ASCII
          or T.61 (as defined in Section 3.5).  CRLF will not be
          present in a valid X.400 field.  Any CRLF present are not
          mapped, but are used as points at which the subject field
          shall be folded, unless an RFC 1522 encoding is used.

     IPMS.Heading.expiry-time
          Mapped to the extended RFC 822 field "Expires:".  The
          replaces the RFC 1327 field "Expiry-Date:".   Reverse
          mapping of the RFC 1327 field may be supported.

     IPMS.Heading.reply-time
          Mapped to the extended RFC 822 field "Reply-By:".

     IPMS.Heading.reply-recipients
          Mapped to "Reply-To:".

     IPMS.Heading.importance
          Mapped to the extended RFC 822 field "Importance:".

     IPMS.Heading.sensitivity
          Mapped to the extended RFC 822 field "Sensitivity:".

     IPMS.Heading.autoforwarded
          Mapped to the extended RFC 822 field "Autoforwarded:".

     The standard extensions (Annex H of X.420 / ISO 10021-7) are
     mapped as follows:

     incomplete-copy
          Mapped to the extended RFC 822 field "Incomplete-Copy:".

     language
          Mapped to the  RFC 822 field "Content-Language:", defined in
          RFC 1766 [7].  This mapping may be made without loss of
          information.

     auto-submitted
          Map to the extended RFC 822 field "Autosubmitted:".

          If the RFC 822 extended header is found, this shall be
     mapped onto an RFC 822 header, as described in Section 5.1.2.




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          If a non-standard extension is found, it shall be discarded,
     unless the gateway understands the extension and can perform an
     appropriate mapping onto an RFC 822 header field.  If extensions
     are discarded, the list is indicated in the extended RFC 822
     field "Discarded-X400-IPMS-Extensions:".

     5.3.4.1.  Mapping the IPMS Body

     The mapping of the IPMS Body is defined in RFC 1494bis.

     5.3.4.2.  Example Message

     An example message, illustrating a number of aspects is given
     below.

































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RFC 1327bis
MIXER                                                DRAFT Version 2.6



     Received: from mhs-relay.ac.uk by bells.cs.ucl.ac.uk via JANET with NIFTP
               id <7906-0@bells.cs.ucl.ac.uk>; Thu, 30 May 1991 18:24:55 +0100
     X400-Received: by mta "mhs-relay.ac.uk" in /PRMD=uk.ac/ADMD= /C=gb/; Relayed;
                    Thu, 30 May 1991 18:23:26 +0100
     X400-Received: by /PRMD=HMG/ADMD=GOLD 400/C=GB/; Relayed;
                    Thu, 30 May 1991 18:20:27 +0100
     Message-Type: Multiple Part
     Date: Thu, 30 May 1991 18:20:27 +0100
     X400-Originator: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
     X400-MTS-Identifier:
          [/PRMD=HMG/ADMD=GOLD 400/C=GB/;PC1000-910530172027-57D8]
     Original-Encoded-Information-Types: ia5
     X400-Content-Type: P2-1984 (2)
     X400-Content-Identifier: Email Problems
     From: Stephen.Harrison@gosip-uk.hmg.gold-400.gb (Tel +44 71 217 3487)
     Message-ID: <PC1000-910530172027-57D8*@MHS>
     To: Jim Craigie <NTIN36@gec-b.rutherford.ac.uk>,
         Tony Bates <tony@ean-relay.ac.uk>,
         Steve Kille <S.Kille@cs.ucl.ac.uk>
     Subject: Email Problems
     Sender: Stephen.Harrison@gosip-uk.hmg.gold-400.gb
     MIME-Version: 1.0
     Content-Type: multipart/mixed; boundary=boundary-1

     --boundary-1
     Content-Type: text/plain; charset=US-ASCII

     Hope you gentlemen.......

     Regards,

     Stephen Harrison
     UK GOSIP Project

      ..... continued on next page











Kille                                                       [page 106]


RFC 1327bis
MIXER                                                DRAFT Version 2.6




     --boundary-1
     Content-Type: message/rfc822

     From: Urs Eppenberger <Eppenberger@verw.switch.ch>
     Message-ID:
       <562*/S=Eppenberger/OU=verw/O=switch/PRMD=SWITCH/ADMD=ARCOM/C=CH/@MHS>
     To: "Stephen.Harrison" <Stephen.Harrison@gosip-uk.hmg.gold-400.gb>
     Cc: kimura@bsdarc.bsd.fc.nec.co.jp
     Subject: Response to Email link
     Content-Type: multipart/mixed; boundary=boundary-2


     --boundary-2

     Dear Mr Harrison......


     --boundary-2--

     --boundary-1--



     5.3.5.  Mappings from an IP Notification

     Because of the service setting, IP Notifications will not usually
     need to be mapped by a MIXER gateway.  A message is generated,
     with the following fields:

     From:
          Set to the IPMS.IPN.ipn-originator.

     To:  Set to the recipient from MTS.MessageSubmissionEnvelope.
          If there have been redirects, the original address shall be
          used.

     Subject:
          Set to the string  "X.400 Inter-Personal Notification" for a
          receipt notification and to "X.400 Inter-Personal
          Notification (failure)" for a non-receipt notification.

     Message-Type:



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          Set to "InterPersonal Notification"

     References:
          Set to IPMS.IPN.subject-ipm

     Discarded-X400-IPMS-Extensions:
          Used for any discarded IPN extensions.

     The following EBNF is defined for the body of the Message.  This
     format is defined to ensure that all information from an
     interpersonal notification is available to the end user in a
     uniform manner.



































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RFC 1327bis
MIXER                                                DRAFT Version 2.6



             ipn-body-format = ipn-description <CRLF>
                             [ ipn-extra-information <CRLF> ]
                             [ ipn-content-return ]

             ipn-description = ipn-receipt / ipn-non-receipt

             ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                      "was received at" receipt-time <CRLF> <CRLF>
                      "This notification was generated"
                      acknowledgement-mode <CRLF>
                      "The following extra information was given:" <CRLF>
                      ipn-suppl <CRLF>

             ipn-non-receipt = "Your message to:"
                     preferred-recipient <CRLF>
                     ipn-reason


             ipn-reason = ipn-discarded / ipn-auto-forwarded

             ipn-discarded = "was discarded for the following reason:"
                             discard-reason <CRLF>

             ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                             [ "The following comment was made:"
                                     auto-comment ]


             ipn-extra-information =
                      "The following information types were converted:"
                      encoded-info

             ipn-content-return = "The Original Message is not available"
                             / "The Original Message follows:"


             preferred-recipient = mailbox
             receipt-time        = date-time
             auto-comment        = printablestring
             ipn-suppl           = printablestring






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RFC 1327bis
MIXER                                                DRAFT Version 2.6



             discard-reason     = "Expired" / "Obsoleted" /
                         "User Subscription Terminated" / "IPM Deleted"

             acknowledgement-mode = "Manually" / "Automatically"

     The mappings for elements of the common fields of IPMS.IPN
     (IPMS.CommonFields) onto this structure and the message header
     are:

     subject-ipm
          Mapped to "References:"

     ipn-originator
          Mapped  to "From:".

     ipn-preferred-recipient
          Mapped to EBNF.preferred-recipient

     conversion-eits
          Mapped to EBNF.encoded-info in EBNF.ipn-extra-information

     The mappings for elements of IPMS.IPN.non-receipt-fields
     (IPMS.NonReceiptFields) are:

     non-receipt-reason
          Used to select between EBNF.ipn-discarded and
          EBNF.ipn-auto-forwarded

     discard-reason
          Mapped to EBNF.discard-reason

     auto-forward-comment
          Mapped to EBNF.auto-comment

     returned-ipm
          This applies only to non-receipt notifications.
          EBNF.ipn-content-return shall always be omitted for receipt
          notifications, and always be present in non-receipt
          notifications.  If present, the second option of
          EBNF.ipn-content-return is chosen, and the message is
          included.  In this case, the message is formatted as
          multipart/mixed, and the returned message included as
          message/rfc822 after the text body part. Otherwise the first



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RFC 1327bis
MIXER                                                DRAFT Version 2.6


          option is chosen.

     The mappings for elements of IPMS.IPN.receipt-fields
     (IPMS.ReceiptFields) are:

     receipt-time
          Mapped to EBNF.receipt-time

     acknowledgement-mode
          Mapped to EBNF.acknowledgement-mode

     suppl-receipt-info
          Mapped to EBNF.ipn-suppl

     An example notification is:

             From: Steve Kille <steve@cs.ucl.ac.uk>
             To: Julian Onions <jpo@computer-science.nottingham.ac.uk>
             Subject: X.400 Inter-personal Notification
             Message-Type: InterPersonal Notification
             References: <1229.614418325@UK.AC.NOTT.CS>
             Date: Wed, 21 Jun 89 08:45:25 +0100

             Your message to: Steve Kille <steve@cs.ucl.ac.uk>
             was automatically forwarded.
             The following comment was made:
                     Sent on to a random destination

             The following information types were converted: g3fax



     5.3.6.  Mappings from the MTS Abstract Service

     This section describes the MTS mappings for User Messages (IPM
     and IPN).  This mapping is defined by specifying the mapping of
     MTS.MessageDeliveryEnvelope.  The following extensions to RFC 822
     are defined to support this mapping:









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RFC 1327bis
MIXER                                                DRAFT Version 2.6



             mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                       / "X400-Originator" ":" mailbox
                       / "X400-Recipients" ":" 1#mailbox
                       / "Original-Encoded-Information-Types" ":"
                                       encoded-info
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Content-Identifier" ":" printablestring
                       / "Priority" ":" priority
                       / "Originator-Return-Address" ":" 1#mailbox
                       / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                       / "Conversion" ":" prohibition
                       / "Conversion-With-Loss" ":" prohibition
                       / "Delivery-Date" ":" date-time
                       / "Discarded-X400-MTS-Extensions" ":"
                                    1#( object-identifier / labelled-integer )


             prohibition     = "Prohibited" / "Allowed"

             mts-msg-id       = "[" global-id ";" *text "]"

             mts-content-type = "P2" /  labelled-integer
                             / object-identifier

             priority        = "normal" / "non-urgent" / "urgent"


     The mappings for each element of MTS.MessageDeliveryEnvelope can
     now be considered.  Where the specified action does not result in
     an extended element being mapped, the criticality associated with
     this element shall be considered.  If the element is marked as
     critical for transfer or for delivery, the message shall be non
     delivered by the gateway because a critical extension cannot be
     correctly handled.

     MTS.MessageDeliveryEnvelope.message-delivery-identifier
          Mapped to the extended RFC 822 field "X400-MTS-Identifier:".

     MTS.MessageDeliveryEnvelope.message-delivery-time
          Discarded, as this time will be represented in an
          appropriate trace element.

     The mappings for elements of



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RFC 1327bis
MIXER                                                DRAFT Version 2.6


     MTS.MessageDeliveryEnvelope.other-fields
     (MTS.OtherMessageDeliveryFields) are:

     content-type
          Mapped to the extended RFC 822 field "X400-Content-Type:".
          The string "P2" is retained for backwards compatibility with
          RFC 987. This shall not be generated, and either the
          EBNF.labelled-integer  or EBNF.object-identifier encoding
          used.

     originator-name
          Mapped to the SMTP originator, and to the extended RFC 822
          field "X400-Originator:".  This is described in
          Section 4.6.2.

     original-encoded-information-types
          Mapped to the extended RFC 822 field
          "Original-Encoded-Information-Types:".

     priority
          Mapped to the extended RFC 822 field "Priority:".

     delivery-flags
          If the conversion-prohibited bit is set, add an extended RFC
          822 field "Conversion:".

     this-recipient-name and other-recipient-names
          The handling of these elements is described in
          Section 4.6.2.

     originally-intended-recipient-name
          The handling of this element is described in Section 4.6.2.

     converted-encoded-information-types
          Discarded.  This information will be mapped in the trace.

     message-submission-time
          Mapped to Date:.

     content-identifier
          Mapped to the extended RFC 822 field
          "X400-Content-Identifier:".  In RFC 1327, this was
          "Content-Identifier:".  This has been changed to avoid
          confusion with MIME defined fields.   Gateways which reverse



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RFC 1327bis
MIXER                                                DRAFT Version 2.6


          map, may support the old field.

     If any extensions
     (MTS.MessageDeliveryEnvelope.other-fields.extensions) are
     present, and they are marked as critical for transfer or
     delivery, then the message shall be rejected.  The extensions
     (MTS.MessageDeliveryEnvelope.other-fields.extensions) are mapped
     as follows.

     conversion-with-loss-prohibited
          If set to
          MTS.ConversionWithLossProhibited.conversion-with-loss-prohibited,
          then add the extended RFC 822 field "Conversion-With-Loss:".

     requested-delivery-method
          Mapped to a comment, as described in Section 4.6.2.2.

     originator-return-address
          Mapped to the extended RFC 822 field
          "Originator-Return-Address:".

     physical-forwarding-address-request
     physical-delivery-modes
     registered-mail-type
     recipient-number-for-advice
     physical-rendition-attributes
     physical-delivery-report-request
     physical-forwarding-prohibited


          These elements are only appropriate for physical delivery.
          They are represented as comments in the "X400-Recipients:"
          field, as described in Section 4.6.2.2.

     originator-certificate
     message-token
     content-confidentiality-algorithm-identifier
     content-integrity-check
     message-origin-authentication-check
     message-security-label
     proof-of-delivery-request

          These elements imply use of security services not available
          in the RFC 822 environment.  If they are marked as critical



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RFC 1327bis
MIXER                                                DRAFT Version 2.6


          for transfer or delivery, then the message shall be
          rejected.  Otherwise they are discarded.

     redirection-history
          This is described in Section 4.6.2.

     dl-expansion-history
          Each element is mapped to an extended RFC 822 field
          "DL-Expansion-History:".  These fileds shall be ordered in
          the message header, so that the most recent expansion comes
          first (same order as trace).

          If any MTS (or MTA) Extensions not specified in X.400 are
     present, and they are marked as critical for transfer or
     delivery, then the message shall be rejected.  If they are not so
     marked, they can safely be discarded.  The list of discarded
     fields shall be indicated in the extended header
     "Discarded-X400-MTS-Extensions:".

     5.3.7.  Mappings from the MTA Abstract Service

     There are some mappings at the MTA Abstract Service level which
     are done for IPM and IPN.  These can be derived from
     MTA.MessageTransferEnvelope.  The reasons for the mappings at
     this level, and the violation of layering are:

     -    Allowing for multiple recipients to share a single RFC 822
          message

     -    Making the X.400 trace information available on the RFC 822
          side

     -    Making any information on deferred delivery available

     The SMTP recipients are calculated from the full list of X.400
     recipients.  This is all of the members of
     MTA.MessageTransferEnvelope.per-recipient-fields being passed
     through the gateway, where the responsibility bit is set.  In
     some cases, a different RFC 822 message would be calculated for
     each recipient, due to differing service requests for each
     recipient.  As discussed in 4.6.2.2, this specification allows
     either for multiple messages to be generated, or for the per-
     recipient information to be discarded.




Kille                                                       [page 115]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     The following EBNF is defined for extended RFC 822 headers:


             mta-field       = "X400-Received" ":" x400-trace
                             / "Deferred-Delivery" ":" date-time
                             / "Latest-Delivery-Time" ":" date-time



             x400-trace       = "by" md-and-mta ";"
                              [ "deferred until" date-time ";" ]
                              [ "converted" "(" encoded-info ")" ";" ]
                              [ "attempted" md-or-mta ";"  ]
                                 action-list
                                 ";" arrival-time


             md-and-mta       = [ "mta" mta "in" ]  global-id
             mta              = word
             arrival-time     = date-time

             md-or-mta        = "MD" global-id
                              / "MTA" mta

             Action-list      = 1#action
             action           = "Redirected"
                              / "Expanded"
                              / "Relayed"
                              / "Rerouted"




          Note the EBNF.mta is encoded as 822.word.  If the character
     set does not allow encoding as 822.atom, the 822.quoted-string
     encoding is used.

          If MTA.PerMessageTransferFields.deferred-delivery-time is
     present, it is used to generate a Deferred-Delivery: field.
     X.400 does not make this information available at the MTS level
     on delivery, because it requires that this service is provided by
     the first MTA. In the event that the first MTA does not provide
     this service, the function may optionally be implemented by the
     gateway: that is, the gateway may hold the message until the time



Kille                                                       [page 116]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     specified in the protocol element.  Thus, the value of this
     element will usually be in the past.  For this reason, the
     extended RFC 822 field is primarily for information.

          If MTA.PerMessageTransferFields.extensions.dl-expansion-
     prohibited is present and set to dl-expansion-probited, the
     gateway may reject that message on the basis that it is unable to
     control distribution list expansion beyond the gateway.   The
     service relating to this is described in Section 2.3.1.2.   This
     approach was not specified in RFC 1327.  If it is found to be
     useful, it may be made mandatory in future versions of MIXER.

          If MTA.PerMessageTransferFields.extensions.recipient-
     reassignment-prohibited is present and set to
     recipeint-reassignment-probited, the gateway may reject that
     message on the basis that it is unable to control distribution
     list expansion beyond the gateway.   The service relating to this
     is described in Section 2.3.1.2.   This approach was not
     specified in RFC 1327.  If it is found to be useful, it may be
     made mandatory in future versions of MIXER.

          Merge MTA.PerMessageTransferFields.trace-information, and
     MTA.PerMessageTransferFields.internal-trace-information to
     produce a single ordered trace list.  If Internal trace from
     other management domains has not been stripped, this may require
     complex interleaving. Where an element of internal trace and
     external trace are identical, except for the MTA in the internal
     trace, only the internal trace element shall be presented. Use
     this to generate a sequence of "X400-Received:" fields. The only
     difference between external trace and internal trace will be the
     extra MTA information in internal trace elements.

          When generating an RFC 822 message all trace fields (X400-
     Received and Received) shall be at the beginning of the header,
     before any other fields.  Trace shall be in chronological order,
     with the most recent element at the front of the message.  This
     ordering is determined from the order of the fields, not from
     timestamps in the trace, as there is no guarantee of clock
     synchronisation.  A simple example trace (external) is:

     X400-Received: by /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ; Relayed ;
             Tue, 20 Jun 89 19:25:11 +0100

     A more complex example (internal):



Kille                                                       [page 117]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     X400-Received: by mta "UK.AC.UCL.CS" in  /PRMD=UK.AC/ADMD=Gold 400/C=GB/ ;
             deferred until  Tue, 20 Jun 89 14:24:22 +0100 ;
             converted (undefined, g3fax) ; attempted MD /ADMD=Foo/C=GB/ ;
             Relayed, Expanded, Redirected ; Tue, 20 Jun 89 19:25:11 +0100


          The gateway itself shall add a single line of trace
     information, indicating MIXER conversion by use of a comment.
     For example:

     Received: from isode.com by isode.com
            (MIXER Conversion following RFC 1327);
            Thu, 2 Jan 1997 14:46:03 +0000


          If SMTP is being used, Appendix A shall also be followed,
     which includes optional mappings to extension parameters.

     5.3.8.  Mappings from Report Delivery

     Delivery reports are mapped at the MTS service level.  This means
     that only reports destined for the MTS user will be mapped.  Some
     additional services are also taken from the MTA service.  X.400
     Delivery Reports are Mapped onto Delivery Status Notifications,
     as defined by NOTARY [28].

     5.3.8.1.  MTS Mappings

     A Delivery Report service will be represented as
     MTS.ReportDeliveryEnvelope, which comprises of per-report-fields
     (MTS.PerReportDeliveryFields) and per-recipient-fields.

     The enclosing message is a MIME message of content type
     multipart/report, with report-type=delivery-status, which is
     generated with the following fields:

     From:
          An administrator at the gateway system.

     To:  A mapping of the
          MTA.ReportTransferEnvelope.report-destination-name.  This is
          also the SMTP recipient.




Kille                                                       [page 118]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     Message-Type:
          Set to "Delivery Report".  This is strictly redundant, but
          retained for backwards compatibility with RFC 1327.

     Subject:
          The EBNF for the subject line is:


             subject-line  = "Delivery-Report" "(" status ")"
                             [ "for" destination ]

             status        = "success" / "failure" / "success and failures"

             destination   = mailbox / "MTA" word


          The subject is intended to give a clear indication as to the
     nature of the message, and summarise its contents. EBNF.status is
     set according to whether the recipients reported on are all
     successes, all failures, or a mixture.  It is common for a report
     to reference a single recipient, in which case a subject line
     giving using all of the options of EBNF.status can be used.  This
     gives useful information to the recipient.  Where information
     varies between reported recpients, the options cannot be used.
     The EBNF.destination is used to indicate the addresses in the
     reports.  If the report is for a single address, EBNF.mailbox is
     used to give the RFC 822 representation of the address.  If all
     of the reported recpients reference the same MTA this is included
     in EBNF.word.   The MTA is determined from the delivery report's
     trace.

          The format of the body of the message follows the NOTARY
     delivery status notification format, and is defined to ensure
     that all information is conveyed to the RFC 822 user in a
     consistent manner.  The format is structured as if it was a
     message coming from the gateway, with three body parts. The first
     body part is ASCII text structured as follows:

     1.   A few lines giving keywords to indicate the original
          message.

     2.   A human summary of the status of each recipient being
          reported on.




Kille                                                       [page 119]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          The second (mandatory)  body part is the NOTARY delivery
     status notification, which contains detailed information
     extracted from the report.  This information may be critical to
     diagnosing an obscure problem.

          The third (optional) body part contains the returned message
     (return of content).  This structure is useful to the RFC 822
     recipient, as it enables the original message to be extracted.
     For negative reports it shall be included if the original message
     is available.  For positive reports headers from the message
     shall be included if the original message is available.

          The first body part containing the user oriented description
     is of type text/plain.  The format of this body part is defined
     below as EBNF.dr-user-info.
































Kille                                                       [page 120]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             dr-user-info = dr-summary <CRLF>
                             dr-recipients <CRLF>
                             dr-content-return


             dr-content-return = "The Original Message is not available"
                  / "The Original Message follows:"

             dr-summary = "This report relates to your message:" <CRLF>
                             content-correlator <CRLF> <CRLF>
                          "of" date-time <CRLF> <CRLF>


             dr-recipients = *(dr-recipient <CRLF> <CRLF>)

             dr-recipient = dr-recip-success / dr-recip-failure

             dr-recip-success =
                             "Your message was successfully delivered to:"
                              mailbox "at" date-time


             dr-recip-failure = "Your message was not delivered to:"
                                     mailbox <CRLF>
                             "for the following reason:" *word

             report-point = [ "mta" mta-name "in" ] global-id
             content-correlator = *word
             mta-name = word


     EBNF.dr-summary
          The EBNF.content-correlator is taken from the content
          correlator (or content identifier if there is no content
          correlator) and the EBNF.date-time from the trace, as
          described in Section 5.3.8.3.  LWSP may be added to improve
          the layout of the body part.

     EBNF.dr-recipients
          There is an element for each recipient in the delivery
          report.  In each case, EBNF.mailbox is taken from the RFC
          822 form of the originally specified recipient, which is
          taken from the originally specified recipient element if



Kille                                                       [page 121]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          present or from the actual recipient.  When reporting
          success, the message delivery time is used to derive
          EBNF.date-time.  When reporting failure, the information
          includes a human readable interpretation of the X.400
          diagnostic and reason codes, and the supplementary
          information.

     EBNF.dr-content-return
          This is set according to whether or not the content is being
          returned.

     The EBNF of this body part is designed for english-speaking
     users.  The language of the strings in the EBNF may be altered.

     The EBNF used in the delivery status notification is:


             dr-per-message-fields =
                       / "X400-Conversion-Date" ":" date-time
                       / "X400-Subject-Submision-Identifier" ":"
                                             mts-msg-id
                       / "X400-Content-Identifier" ":" printablestring
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Original-Encoded-Information-Types" ":"
                                     encoded-info
                       / "X400-Originator-and-DL-Expansion-History" ":"
                                     mailbox ";" date-time ";"
                       / "X400-Reporting-DL-Name" ":" mailbox
                       / "X400-Content-Correlator" ":" content-correlator
                       / "X400-Recipient-Info" ":" recipient-info
                       / "X400-Subject-Intermediate-Trace-Information" ":"
                                               x400-trace
                       / dr-extensions














Kille                                                       [page 122]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             dr-per-recipient-fields =
                       / "X400-Redirect-Recipient" ":" "x400" ";" std-or
                       / "X400-Mapped-Redirect-Recipient" ":" "rfc822" ";" mailbox
                       / "X400-Converted-EITs" ":" encoded-info ";"
                       / "X400-Delivery-Time" ":" date-time
                       / "X400-Type-of-MTS-User" ":" labelled-integer
                       / "X400-Last-Trace" ":" [ encoded-info ] date-time
                       / "X400-Supplementary-Info" ":"
                             <"> printablestring <"> ";"
                       / "X400-Redirection-History" ":" redirect-history-item
                       / "X400-Physical-Forwarding-Address" ":" mailbox
                       / "X400-Originally-Specified-Recipient-Number" ":"
                             integer
                       / dr-extensions

             dr-extensions = "X400-Discarded-DR-Extensions" ":"
                               1# (object-identifier / labelled-integer)


             dr-diagnostic = "Reason" labelled-integer-2
                             [ ";" "Diagnostic" labelled-integer-2 ]


     A body part of type delivery status, as defined by NOTARY, is
     generated.  MIXER extends this delivery status notification (DSN)
     specification, by defining additional per message fields in
     EBNF.dr-per-message-fields and additional per recipient fields in
     EBNF.dr-per-recipient-fields.   These are used as extensions to
     DSN.per-message-fields and DSN.per-recipient-fields.  MIXER also
     defines a new NOTARY address type "x400", with encoding of
     EBNF.std-or.   A directory name may be inluded as an RFC 822
     comment.

     The following DSN.per-message-fields are always generated:

     DSN.reporting-mta-field
          The DSN.mta-name-type is set to "x400", and this string is
          reserved by MIXER.  The DSN.mta-name has its syntax
          specified by EBNF.report-point, with the information derived
          from the first element of the DR's trace.

     DSN.arrival-date-field
          This is derived from the date of the



Kille                                                       [page 123]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          MTA.PerRecipientReportTransferFields.last-trace-info.arrival-time
          of the first recipient in the report.

          The following two EBNF.per-message-fields are generated by
     the MIXER gateway:

     DSN.dsn-gateway-field
          The type is set to "dns" and the  domain  set to the local
          domain of the gateway.

     X400-Conversion-Date:
          The EBNF.date-time is set to the time of the MIXER
          conversion.

          The elements of MTS.ReportDeliveryEnvelope.per-report-fields
     are mapped as follows onto the DSN per message fields as follows:

     subject-submission-identifier
          Mapped to DSN.original-envelope-id-field.  The encoding of
          this MTS Identifier follows the format EBNF.mts-msg-id.

     content-identifier
          Mapped to X400-Content-Identifier:

     content-type
          Mapped to X400-Content-Type:

     original-encoded-information-types
          Mapped to X400-Encoded-Info:

     The extensions from
     MTS.ReportDeliveryEnvelope.per-report-fields.extensions are
     mapped as follows:

     originator-and-DL-expansion-history
          Each element is mapped to an
          "X400-Originator-and-DL-Expansion-History:"  They shall be
          ordered so that the most recent expansion comes first in the
          header (same order as trace).

     reporting-DL-name
          Mapped to X400-Reporting-DL-Name:

     content-correlator



Kille                                                       [page 124]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          If the content correlator starts with the string
          "SMTP/NOTARY ENVID: ", then the remainder of the content
          correlator is mapped to the DSN original-envelope-id field.
          If this is not the case, the content correlator is mapped to
          X400-Content-Correlator:, provided that the encoding is
          IA5String (this will always be the case).

     message-security-label
     reporting-MTA-certificate
     report-origin-authentication-check

          These security parameters will not be present unless there
          is an error in a remote MTA.  If they are present, they
          shall be discarded in preference to discarding the whole
          report.  They shall be listed in the X400-Discarded-DR-
          Extensions: field.

     If there are any other DR extensions, they shall also be
     discarded and listed in the X400-Discarded-DR-Extensions: field.

     For each element of
     MTS.ReportDeliveryEnvelope.per-recipient-fields, a set of
     DSN.per-recipient-fields is generated.  The fields are filled in
     as follows:

     actual-recipient-name
          If originally-intended-recipient-name is not present,
          generate a DSN.original-recipient-field fields, with
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate a DSN.final-recipient-field field, which holds
          the X.400 representation of the same address.  If the
          directory name is present, it shall be added as a trailing
          comment in the X.400 form.

          If originally-intended-recipient-name is present, generate
          an "X400-Mapped-Redirect-Recipient:" field, with
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate an "X400-Redirect-Recipient:" field, which
          holds the X.400 representation of the same address.  If the
          directory name is present, it shall be added as a trailing
          comment in the X.400 form.




Kille                                                       [page 125]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     report
          If it is MTS.Report.delivery, then set DSN.action-field to
          "delivered", and set "X400-Delivery-Time:" and
          "X400-Type-of-MTS-User:" from the information in the report.
          DSN.status field is set to "2.0.0".

          If it is MTS.Report.non-delivery, then set DSN.action-field
          to "failed".   DSN.diagnostic-code-field is encoded
          according to the syntax EBNF.dr-diagnostic, with the
          labelled integers set from the reason and diagnostic codes.
          DSN.status-field is derived from the reason and diagnostic
          codes, as described below.

     converted-encoded-information-types
          Set X400-Converted-EITs:

     originally-intended-recipient
          Generate a DSN.final-recipient-field field, with
          DSN.address-type of "rfc822", and with an RFC 822 mailbox
          generated from the address encoded as specified by NOTARY.
          Also generate a DSN.original-recipient-field field, which
          holds the X.400 representation of the same address.  If the
          directory name is present, it shall be added as a trailing
          comment in the X.400 form.

     supplementary-info
          Set X400-Supplementary-Info:

     redirection-history
          Generate an "X400-Redirection-History:" field for each
          redirect history element.  The fields are ordered with the
          earliest redirect first.

     physical-forwarding-address
          Set X400-Physical-Forwarding-Address as a mailbox, with
          directory name in comment if present.

     recipient-certificate
          Discard

     proof-of-delivery
          Discard

     Any unknown extensions shall be discarded, irrespective of



Kille                                                       [page 126]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     criticality.  All discarded extensions shall be included in a
     "X400-Discarded-DR-Extensions:" field.

          The number from the
     MTA.PerRecipientReportTransferFields.originally-specified-recipient-number
     shall be mapped to "X400-Originally-Specified-Recipient-Number:",
     in order to facilitate reverse mapping of delivery reports.

          The original message shall be included in the delivery
     status notification if it is available. The original message will
     usually be available at the gateway, as discussed in Section 5.2.
     If the original message is available, but is not a legal message
     format, a dump of the ASN.1 may be included, encoded as
     application/octet-string.  This is recommended, but not required.

          Where the original message is included, it shall be encoded
     according to the MIME specifications as content type
     message/rfc822.

     5.3.8.2.  Status Code Mappings

     This section defines the mappings from X.400 diagnostic and
     status codes to the NOTARY Status field.

     C/D     X400 meaning                            DSN code        Means

     0/Any   Transfer failure (may be temporary)     4.4.0 Other net/route
     1/Any   Unable to transfer                      5.0.0 Other, unknown
     2/Any   Conversion not performed                5.6.3 Conv not supported
     3/Any   Physical rendition not performed        5.6.0 Other media error
     4/Any   Physical delivery not performed         5.1.0 Other address status
     5/Any   Restricted delivery                     5.7.1
     6/Any   Directory operation unsuccessful        5.4.3 Routing server failure
     7/Any   Deferred delivery not performed         5.3.3 Not capable













Kille                                                       [page 127]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     1/0     Unrecognized OR name                    5.1.1
     1/1     Ambiguous OR name                       5.1.4
     1/2     MTS congestion                          4.3.1
     1/3     Loop detected                           5.4.6
     1/4     Recipient unavailable                   4.2.1
     1/5     Delivery time expired                   4.4.7
     1/6     Encoded information types unsupported   5.6.1 Media unsupp.
     1/7     Content too long                        5.2.3
     2/8     Conversion impractical                  5.6.3
     2/9     Conversion prohibited                   5.6.3
     1/10    Implicit conversion not subscribed      5.6.3
     1/11    Invalid arguments                       5.5.2
     1/12    Content syntax error                    5.5.2
     1/13    Size constraint violation               5.5.2
     1/14    Protocol violation                      5.5.0
     1/15    Content type not supported              5.6.1 Media unsupp.
     1/16    Too many recipients                     5.5.3
     1/17    No bilateral agreement                  5.4.4
     1/18    Unsupported critical function           5.3.3 System not capable
     2/19    Conversion with loss prohibited         5.6.2
     2/20    Line too long                           5.6.0
     2/21    Page split                              5.6.0
     2/22    Pictorial symbol loss                   5.6.2
     2/23    Punctuation symbol loss                 5.6.2
     2/24    Alphabetic character loss               5.6.2
     2/25    Multiple information loss               5.6.2
     1/26    Recipient reassignment prohibited       5.4.0 Undefined net/route
     1/27    Redirection loop detected               5.4.6
     1/28    DL expansion prohibited                 5.7.2
     1/29    No DL submit permission                 5.7.1 Delivery not authorized
     1/30    DL expansion failure                    4.2.4
     4/31    Physical rendition attrs not supported  5.6.0 Undefined media error
     4/32-45 Various physical mail stuff             5.1.0 Other address status
     1/43    New address unknown                     5.1.6 Destination mbox moved
     1/46    Secure messaging error                  5.7.0 Other security status
     2/47    Unable to downgrade                     5.3.3 System not capable
     0/48    Unable to complete transfer             5.3.4 Message too big
     0/49    Transfer attempts limit reached         4.4.7 Delivery time expired


     5.3.8.3.  MTA Mappings

          The single SMTP recipient is constructed from



Kille                                                       [page 128]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     MTA.ReportTransferEnvelope.report-destination-name, using the
     mappings of Chapter 4.  Unlike with a user message, this
     information is not available at the MTS level.

     The following additional mappings are made, which results in
     fields in the outer header of the DSN.

     MTA.ReportTransferEnvelope.report-destination-name
          This is used to generate the To: field.

     MTA.ReportTransferEnvelope.identifier
          Mapped to the extended RFC 822 field "X400-MTS-Identifier:".
          It may also be used to derive a "Message-Id:" field.

     MTA.ReportTransferEnvelope.trace-information
          and
     MTA.ReportTransferEnvelope.internal-trace-information

          Mapped onto the extended RFC 822 field "X400-Received:", as
          described in Section 5.3.7.  Date: is generated from the
          first element of trace.

     The following additional mappings are made, which result in per
     message fields in the DSN body part:

     MTA.PerRecipientReportTransferFields.last-trace-information
          Mapped to X400-Last-Trace:".

     MTA.PerReportTransferFields.subject-intermediate-trace-
          information Mapped to
          "X400-Subject-Intermediate-Trace-Information:". These fields
          are ordered so that the most recent trace element comes
          first.

     5.3.8.4.  Example Delivery Reports

     This section contains sample delivery reports.   These are the
     same examples used in RFC 1327, and so they also illustrate the
     changes between RFC 1327 and this document.  Example Delivery
     Report 1:







Kille                                                       [page 129]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
        via Delivery Reports Channel id <27699-0@bells.cs.ucl.ac.uk>;
        Thu, 7 Feb 1991 15:48:39 +0000
     From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
     To: S.Kille@cs.ucl.ac.uk
     Subject: Delivery Report (failure) for H.Hildegard@bbn.com
     Message-Type: Delivery Report
     Date: Thu, 7 Feb 1991 15:48:39 +0000
     Message-ID: <"bells.cs.u.694:07.01.91.15.48.34"@cs.ucl.ac.uk>
     X400-Content-Identifier: Greetings.
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
         boundary=boundary-1

     --boundary-1

     This report relates to your message:
             Greetings.

             of Thu, 7 Feb 1991 15:48:20 +0000


     Your message was not delivered to
             H.Hildegard@bbn.com for the following reason:
             Bad Address
             MTA 'bbn.com' gives error message  (USER) Unknown user name in
             "H.Hildegard@bbn.com"

     The Original Message follows:


     --boundary-1
     content-type: message/delivery-status













Kille                                                       [page 130]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     Reporting-MTA: x400;  bells.cs.ucl.ac.uk in /PRMD=uk.ac/ADMD=gold 400/C=gb/
     Arrival-Date: Thu, 7 Feb 1991 15:48:34 +0000
     DSN-Gateway: dns;  bells.cs.ucl.ac.uk
     X400-Conversion-Date: Thu, 7 Feb 1991 15:48:40 +0000
     Original-Envelope-Id:
              [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1803.665941698@UK.AC.UCL.CS>]
     X400-Content-Identifier: Greetings.
     X400-Subject-Intermediate-Trace-Information:  /PRMD=uk.ac/ADMD=gold 400/C=gb/;
              arrival Thu, 7 Feb 1991 15:48:20 +0000 action Relayed
     X400-Subject-Intermediate-Trace-Information:  /PRMD=uk.ac/ADMD=gold 400/C=gb/;
              arrival Thu, 7 Feb 1991 15:48:18 +0000 action Relayed



     Original-Recipient: rfc822; H.Hildegard@bbn.com
     Final-Recipient: x400;
       /RFC-822=H.Hildegard(a)bbn.com/OU=cs/O=ucl/PRMD=uk.ac/ADMD=gold 400/C=gb/;
     Action: failure
     Status: 5.1.1
     Diagnostic-Code: x400; Reason 1 (Unable-To-Transfer);
          Diagnostic 0 (Unrecognised-ORName)
     X400-Last-Trace: (ia5) Thu, 7 Feb 1991 15:48:18 +0000;
     X400-Originally-Specified-Recipient-Number: 1
     X400-Supplementary-Info: "MTA 'bbn.com' gives error message  (USER)
         Unknown user name in "H.Hildegard@bbn.com"";





















Kille                                                       [page 131]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     --boundary-1
     Content-Type: message/rfc822

     Received: from glenlivet.cs.ucl.ac.uk by bells.cs.ucl.ac.uk
       with SMTP inbound id <27689-0@bells.cs.ucl.ac.uk>;
       Thu, 7 Feb 1991 15:48:21 +0000
     To: H.Hildegard@bbn.com
     Subject: Greetings.
     Phone: +44-71-380-7294
     Date: Thu, 07 Feb 91 15:48:18 +0000
     Message-ID: <1803.665941698@UK.AC.UCL.CS>
     From: Steve Kille <S.Kille@cs.ucl.ac.uk>


     Steve

     --boundary-1--





























Kille                                                       [page 132]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     Example Delivery Report 2:

     Received: from cs.ucl.ac.uk by bells.cs.ucl.ac.uk
       via Delivery Reports Channel id <27718-0@bells.cs.ucl.ac.uk>;
       Thu, 7 Feb 1991 15:49:11 +0000
     X400-Received: by mta "bells.cs.ucl.ac.uk" in /PRMD=uk.ac/ADMD=gold 400/C=gb/;
       Relayed; Thu, 7 Feb 1991 15:49:08 +0000
     X400-Received: by /PRMD=DGC/ADMD=GOLD 400/C=GB/; Relayed;
       Thu, 7 Feb 1991 15:48:40 +0000
     From: UCL-CS MTA <postmaster@cs.ucl.ac.uk>
     To: S.Kille@cs.ucl.ac.uk
     Subject: Delivery Report (failure) for
              j.nosuchuser@dle.cambridge.DGC.gold-400.gb
     Message-Type: Delivery Report
     Date: Thu, 7 Feb 1991 15:46:11 +0000
     Message-ID: <"DLE/910207154840Z/000"@cs.ucl.ac.uk>
     X400-Content-Identifier: A useful mess...
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
         boundary=boundary-1

     --boundary-1

     This report relates to your message:
             A useful mess...

             of Thu, 7 Feb 1991 15:43:20 +0000


     Your message was not delivered to
             j.nosuchuser@dle.cambridge.DGC.gold-400.gb
             for the following reason:
             Bad Address
             DG 21187: (CEO POA) Unknown addressee.

     The Original Message is not available










Kille                                                       [page 133]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



     --boundary-1
     content-type: message/delivery-status


     Reporting-MTA: x400; /PRMD=DGC/ADMD=GOLD 400/C=GB/
     Arrival-Date: Thu, 7 Feb 1991 15:48:40 +0000
     DSN-Gateway: dns;  bells.cs.ucl.ac.uk
     X400-Conversion-Date: Thu, 7 Feb 1991 15:49:12 +0000
     Original-Envelope-Id:
        [/PRMD=uk.ac/ADMD=gold 400/C=gb/;<1796.665941626@UK.AC.UCL.CS>]
     X400-Content-Identifier: A useful mess...



     Original-Recipient: rfc822; j.nosuchuser@dle.cambridge.DGC.gold-400.gb
     Final-Recipient: x400;
       /I=j/S=nosuchuser/OU=dle/O=cambridge/PRMD=DGC/ADMD=GOLD 400/C=GB/
     Action: failure
     Status: 5.1.1
     Diagnostic-Code: x400; Reason 1 (Unable-To-Transfer);
          Diagnostic 0 (Unrecognised-ORName)
     X400-Supplementary-Info: "DG 21187: (CEO POA) Unknown addressee."
     X400-Originally-Specified-Recipient-Number: 1

     --boundary-1--



     5.3.9.  Probe

     This is an MTS internal issue.  Any probe shall be serviced by
     the gateway, as there is no equivalent RFC 822 functionality.
     The value of the reply is dependent on whether the gateway could
     service an MTS Message with the values specified in the probe.
     The reply shall make use of MTS.SupplementaryInformation to
     indicate that the probe was serviced by the gateway.










Kille                                                       [page 134]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     Appendix A - Mappings Specific to SMTP

     This Appendix is specific to the Simple Mail Transfer  Protocol
     (RFC 821).  It describes specific changes in the context of this
     protocol.  When MIXER is used with SMTP, conformance to this
     appendix is mandatory.


     1.  Probes

     When servicing a probe, as described in section 5.3.9, use may be
     made of the SMTP VRFY command to increase the accuracy of
     information contained in the delivery report.

     2.  Long Lines

     SMTP is a text oriented protocol, and is required to support a
     line length of at least 1000 characters.   Some implementations
     do not support line lengths greater than 1000 characters.   This
     can cause problems.  Where body parts have long lines, it is
     recommended to use a MIME encoding that folds lines (quoted
     printable).

     3.  SMTP Extensions

     There are several RFCs that specify extensions to SMTP. Most of
     these are not relevant to MIXER.  The NOTARY work to support
     delivery report defines extensions which are relevant [29].  Use
     of these extensions by a MIXER gateway is optional.  If these
     extensions are used, they shall be used in the manner described
     below.

     3.1.  SMTP Extension mapping to X.400

     Mappings are defined for the following extensions:

     NOTIFY
          This is used to set the report and non-delivery bits of
          MTA.PerRecipientMessageTransferFields.per-recipient-indicators.
          If the value is NEVER, both bits are zero.  If SUCCESS is
          present, the report bit is set.  Otherwise, the non-
          delivery-report bit is set.  If the gateway uses the NOTIFY
          command, it shall perform this mapping in all cases.




Kille                                                       [page 135]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     ORCPT
          If the address type of the original recipient is "x400" or
          "rfc822", this may be used at the MTS level, to generate an
          element of redirection history, with the redirection date
          being the date of conversion and the reason set to "alias".

     ENVID
          If present, this may be used to generate a content
          correlator.   This is used rather than the MTS Identifier,
          as the ENVID is unique for the UA only and is likely to be
          too large to map to an MTS identifier. The content
          correlator is encoded as an IA5 String containing the ENVID
          and prefixed by the string:

                  "SMTP/NOTARY ENVID: "

          If the ENVID starts with the string "X400-MTS-Identifier: ",
          then this ENVID was generated from an X.400 MTS Identifier.
          The reverse mapping defined in Section 3.2 of Appendix A
          shall not be used, as this may cause problems in certain
          situations (e.g., where the message was expanded by an
          Internet mailing list).

     3.2.  X.400 Mapping to SMTP Extensions

     The following extensions may be used as a part of the MIXER
     mapping:

     NOTIFY
          The originator-report and originator-non-delivery-report
          bits of
          MTA.PerRecipientMessageTransferFields.per-recipient-indicators
          determine how this is used.   If both bits are zero, the
          parameter is NEVER.  If the report bit is set, SUCCESS is
          used.   Otherwise, FAILURE is used.  If this is done, the
          gateway shall not generate a delivery report for this
          recipient, unless this is needed in the case where the
          originating MTA service report requirements differ from the
          user requirements.   Additional originating MTA
          requrirements are satisfied by the gateway.

     ORCPT
          If the
          MTS.perRecipientDeliveryFields.originally-intended-recipient-name



Kille                                                       [page 136]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          is present, the ORCPT command may be used to carry this
          value, using the "x400" syntax.

     ENVID
          This may be generated, with the value taken from the
          MTS.MessageDeliveryEnvelope.message-delivery-identifer.  If
          this is done, it shall be encoded as EBNF.mts-msg-id,
          preceded by the string "X400-MTS-Identifier: ".

     RET
          If
          MTA.PerMessageTransferFields.per-message-indicators.content-return-request
          is set to FALSE, the parameter RET may be set to HDRS, to
          specify return of headers only.

































Kille                                                       [page 137]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


          Appendix B - Mapping with X.400(1984)


     This appendix defines modifications to the  mapping for use with
     X.400(1984).

          The X.400(1984) protocols are a proper subset of
     X.400(1988).  When mapping from X.400(1984) to RFC 822, no
     changes to this specification are needed.

          When mapping from RFC 822 to X.400(1984), no use can be made
     of 1988 specific features.   No use of such features is made at
     the MTS level.  The heading extension feature is used at the IPMS
     level, and this shall be replaced by the RFC 987 approach.  All
     header information which would usually be mapped into the
     rfc-822-heading-list extension is mapped into a single IA5 body
     part, which is the first body part in the message.  This body
     part will start with the string "RFC-822-Headers:" as the first
     line.  The headers then follow this line.  This specification
     requires correct reverse mapping of this format, either from 1988
     or 1984.  RFC 822 extended headers which could be mapped into
     X.400(1988) elements, are also mapped to the body part.

          In an environment where RFC 822 is of major importance, it
     may be desirable for downgrading to consider the case where the
     message was originated in an RFC 822 system, and mapped according
     to this specification.  The rfc-822-heading-list extension may be
     mapped according to this appendix.

          When parsing std-or, the following restrictions shall be
     observed:

     -    Only the 84/88 attributes identified in the table in
          Section 4.2 are present.

     -    No teletex encoding is allowed.

     If an address violates this, it shall be treated as an RFC 822
     address, which will usually lead to encoding as a DDA "RFC-822".

          It is possible that attributes of zero length may be present
     in an OR Address.  This is not legal in 1988, except for ADMD
     where the case is explicitly described in Section 4.3.5.
     Attributes of zero length are deprecated (the attribute shall be



Kille                                                       [page 138]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     omitted), and will therefore be unusual.  However, some systems
     generate them and rely on them.  Therefore, any null attribute
     shall be enoded using the std-or encoding (e.g., /O=/).

          If a non-Teletex Common Name (CN) is present, it shall be
     mapped onto a Domain Defined Attribute "Common".  This is in line
     with RFC 1328 on X.400 1988 to 1984 downgrading [22].

          This specification defines a mapping of the Internet message
     framework to X.400.  Body part mappings are defined in RFC
     1494bis [6], which relies on X.400(88) features.   Downgrading to
     X.400(84) for body parts is defined in RFC 1496 (HARPOON), which
     shall be followed in the context of this appendix [5].


































Kille                                                       [page 139]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     Appendix C - RFC 822 Extensions for X.400 access

     This appendix defines a number of optional mappings which may be
     provided to give access from RFC 822 to a number of X.400
     services.  These mappings are beyond the basic scope of this
     specification.  There has been a definite demand to use extended
     RFC 822 as a mechanism to access X.400, and these extensions
     provide access to certain features.  If this functionality is
     provided, this appendix shall be followed.  The following
     headings are defined:

             extended-heading =
                 "Prevent-NonDelivery-Report" ":"
                 / "Generate-Delivery-Report" ":"
                 / "Alternate-Recipient" ":" prohibition
                 / "Disclose-Recipients" ":"  prohibition
                 / "X400-Content-Return" ":" prohibition



     Prevent-NonDelivery-Report and Generate-Delivery-Report allow
     setting of
     MTS.PerRecipientSubmissionFields.originator-report-request.  The
     setting will be the same for all recipients.

          Alternate-Recipient, Disclose-Recipients, and X400-Content-
     Return allow for override of the default settings for
     MTS.PerMessageIndicators.

          Use of NOTARY mechanisms is a preferred meachanism for
     controlling these parameters.
















Kille                                                       [page 140]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     Appendix D - Object Identifier Assignment


     The following Object Identifiers shall be used.

     internet ::= OBJECT IDENTIFIER  { iso org(3) dod(6) 1 } -- from RFC 1155

     mail OBJECT IDENTIFIER ::= { internet 7 }  -- IANA assigned

     mixer OBJECT IDENTIFIER ::= { mail mixer(1) } -- inherited from RFC 1495
     mixer-core OBJECT IDENTIFIER ::= { mixer core(3) }

     id-rfc-822-field-list OBJECT IDENTIFIER ::= {mixer-core 2}
     id-dsn-header-list OBJECT IDENTIFIER ::= {mixer-core 3}
     id-dsn-field-list OBJECT IDENTIFIER ::= {mixer-core 4}

     eit-mixer OBJECT IDENTIFIER ::= {mixer-core 5}
                     -- the MIXER pseudo-EIT

     This object identifier for id-rfc-822-field-list is different to
     the one assigned in RFC 1327, which was erroneous.


























Kille                                                       [page 141]


RFC 1327bis
MIXER                                                DRAFT Version 2.6


     Appendix E - BNF Summary



             boolean = "TRUE" / "FALSE"


             numericstring = *(DIGIT / " ")


             printablestring  = *( ps-char )
             ps-restricted-char      = 1DIGIT /  1ALPHA / " " / "'" / "+"
                                / "," / "-" / "." / "/" / ":" / "=" / "?"
             ps-delim         = "(" / ")"
             ps-char          = ps-delim / ps-restricted-char


             ps-encoded       = *( ps-restricted-char / ps-encoded-char )
             ps-encoded-char  = "(a)"               ; (@)
                              / "(p)"               ; (%)
                              / "(b)"               ; (!)
                              / "(q)"               ; (")
                              / "(u)"               ; (_)
                              / "(l)"               ; "("
                              / "(r)"               ; ")"
                              / "(" 3DIGIT ")"


             teletex-string   = *( ps-char / t61-encoded )
             t61-encoded      = "{" 1* t61-encoded-char "}"
             t61-encoded-char = 3DIGIT


             teletex-and-or-ps = [ printablestring ] [ "*" teletex-string ]


             labelled-integer ::= [ key-string ] "(" numericstring ")"

             labelled-integer-2 ::= [ numericstring ] "(" key-string ")"

             key-string      = *key-char
             key-char        = <a-z, A-Z, 0-9, and "-">





Kille                                                       [page 142]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             object-identifier  ::= oid-comp object-identifier
                             | oid-comp

             oid-comp ::= [ key-string ] "(" numericstring ")"


             encoded-info    = 1#encoded-type

             encoded-type    = built-in-eit / object-identifier

             built-in-eit    = "Undefined"         ; undefined (0)
                             / "Telex"             ; tLX (1)
                             / "IA5-Text"          ; iA5Text (2)
                             / "G3-Fax"            ; g3Fax (3)
                             / "TIF0"              ; tIF0 (4)
                             / "Teletex"           ; tTX (5)
                             / "Videotex"          ; videotex (6)
                             / "Voice"             ; voice (7)
                             / "SFD"               ; sFD (8)
                             / "TIF1"              ; tIF1 (9)



             encoded-pn      = [ given "." ] *( initial "." ) surname

             given           = 2*<ps-char not including ".">

             initial         = ALPHA

             surname         = printablestring


             std-or-address  = 1*( "/" attribute "=" value ) "/"
             attribute       = standard-type
                             / "RFC-822"
                             / dd-key "." std-printablestring










Kille                                                       [page 143]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             std-or-address-input =  [ sep pair ] sep  pair *( sep pair )
                                    sep  [ pair sep ]

             sep             = "/" / ";"
             pair            = input-attribute "=" value
             input-attribute = attribute
                             / dd-key ":" std-printablestring



             standard-type   = key-string

             dd-key          = key-string

             value           = std-printablestring

             std-printablestring
                             = *( std-char / std-pair )

             std-char        = <"{", "}", "*", and any ps-char
                                             except "/" and "=" >
             std-pair        = "$" ps-char


             global-id = std-or-address



             mta-field       = "X400-Received" ":" x400-trace
                             / "Deferred-Delivery" ":" date-time
                             / "Latest-Delivery-Time" ":" date-time



             x400-trace       = "by" md-and-mta ";"
                              [ "deferred until" date-time ";" ]
                              [ "converted" "(" encoded-info ")" ";" ]
                              [ "attempted" md-or-mta ";"  ]
                                 action-list
                                 ";" arrival-time






Kille                                                       [page 144]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             md-and-mta       = [ "mta" mta "in" ]  global-id
             mta              = word
             arrival-time     = date-time

             md-or-mta        = "MD" global-id
                              / "MTA" mta

             Action-list      = 1#action
             action           = "Redirected"
                              / "Expanded"
                              / "Relayed"
                              / "Rerouted"


































Kille                                                       [page 145]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             dr-user-info = dr-summary <CRLF>
                             dr-recipients <CRLF>
                             dr-content-return


             dr-content-return = "The Original Message is not available"
                  / "The Original Message follows:"

             dr-summary = "This report relates to your message:" <CRLF>
                             content-correlator <CRLF> <CRLF>
                          "of" date-time <CRLF> <CRLF>


             dr-recipients = *(dr-recipient <CRLF> <CRLF>)

             dr-recipient = dr-recip-success / dr-recip-failure

             dr-recip-success =
                             "Your message was successfully delivered to:"
                              mailbox "at" date-time


             dr-recip-failure = "Your message was not delivered to:"
                                     mailbox <CRLF>
                             "for the following reason:" *word

             report-point = [ "mta" mta-name "in" ] global-id
             content-correlator = *word
             mta-name = word

















Kille                                                       [page 146]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             dr-per-message-fields =
                       / "X400-Conversion-Date" ":" date-time
                       / "X400-Subject-Submision-Identifier" ":"
                                             mts-msg-id
                       / "X400-Content-Identifier" ":" printablestring
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Original-Encoded-Information-Types" ":"
                                     encoded-info
                       / "X400-Originator-and-DL-Expansion-History" ":"
                                     mailbox ";" date-time ";"
                       / "X400-Reporting-DL-Name" ":" mailbox
                       / "X400-Content-Correlator" ":" content-correlator
                       / "X400-Recipient-Info" ":" recipient-info
                       / "X400-Subject-Intermediate-Trace-Information" ":"
                                               x400-trace
                       / dr-extensions


             dr-per-recipient-fields =
                       / "X400-Redirect-Recipient" ":" "x400" ";" std-or
                       / "X400-Mapped-Redirect-Recipient" ":" "rfc822" ";" mailbox
                       / "X400-Converted-EITs" ":" encoded-info ";"
                       / "X400-Delivery-Time" ":" date-time
                       / "X400-Type-of-MTS-User" ":" labelled-integer
                       / "X400-Last-Trace" ":" [ encoded-info ] date-time
                       / "X400-Supplementary-Info" ":"
                             <"> printablestring <"> ";"
                       / "X400-Redirection-History" ":" redirect-history-item
                       / "X400-Physical-Forwarding-Address" ":" mailbox
                       / "X400-Originally-Specified-Recipient-Number" ":"
                             integer
                       / dr-extensions

             dr-extensions = "X400-Discarded-DR-Extensions" ":"
                               1# (object-identifier / labelled-integer)


             dr-diagnostic = "Reason" labelled-integer-2
                             [ ";" "Diagnostic" labelled-integer-2 ]







Kille                                                       [page 147]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             mts-field = "X400-MTS-Identifier" ":" mts-msg-id
                       / "X400-Originator" ":" mailbox
                       / "X400-Recipients" ":" 1#mailbox
                       / "Original-Encoded-Information-Types" ":"
                                       encoded-info
                       / "X400-Content-Type" ":" mts-content-type
                       / "X400-Content-Identifier" ":" printablestring
                       / "Priority" ":" priority
                       / "Originator-Return-Address" ":" 1#mailbox
                       / "DL-Expansion-History" ":" mailbox ";" date-time ";"
                       / "Conversion" ":" prohibition
                       / "Conversion-With-Loss" ":" prohibition
                       / "Delivery-Date" ":" date-time
                       / "Discarded-X400-MTS-Extensions" ":"
                                    1#( object-identifier / labelled-integer )


             prohibition     = "Prohibited" / "Allowed"

             mts-msg-id       = "[" global-id ";" *text "]"

             mts-content-type = "P2" /  labelled-integer
                             / object-identifier

             priority        = "normal" / "non-urgent" / "urgent"





















Kille                                                       [page 148]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             ipn-body-format = ipn-description <CRLF>
                             [ ipn-extra-information <CRLF> ]
                             [ ipn-content-return ]

             ipn-description = ipn-receipt / ipn-non-receipt

             ipn-receipt = "Your message to:" preferred-recipient <CRLF>
                      "was received at" receipt-time <CRLF> <CRLF>
                      "This notification was generated"
                      acknowledgement-mode <CRLF>
                      "The following extra information was given:" <CRLF>
                      ipn-suppl <CRLF>

             ipn-non-receipt = "Your message to:"
                     preferred-recipient <CRLF>
                     ipn-reason


             ipn-reason = ipn-discarded / ipn-auto-forwarded

             ipn-discarded = "was discarded for the following reason:"
                             discard-reason <CRLF>

             ipn-auto-forwarded = "was automatically forwarded." <CRLF>
                             [ "The following comment was made:"
                                     auto-comment ]


             ipn-extra-information =
                      "The following information types were converted:"
                      encoded-info

             ipn-content-return = "The Original Message is not available"
                             / "The Original Message follows:"


             preferred-recipient = mailbox
             receipt-time        = date-time
             auto-comment        = printablestring
             ipn-suppl           = printablestring






Kille                                                       [page 149]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             discard-reason     = "Expired" / "Obsoleted" /
                         "User Subscription Terminated" / "IPM Deleted"

             acknowledgement-mode = "Manually" / "Automatically"


             ipms-field = "Supersedes" ":" 1*msg-id
                        / "Expires" ":" date-time
                        / "Reply-By" ":" date-time
                        / "Importance" ":" importance
                        / "Sensitivity" ":" sensitivity
                        / "Autoforwarded" ":" boolean
                        / "Incomplete-Copy" ":"
                        / "Content-Language" ":" 1#language
                        / "Message-Type" ":" message-type
                        / "Discarded-X400-IPMS-Extensions" ":" 1#object-identifier
                        / "Autosubmitted" ":" autosubmitted



             importance      = "low" / "normal" / "high"


             sensitivity     = "Personal" / "Private" /
                                    "Company-Confidential"

             language        = 2*ALPHA [ "(" language-description ")" ]
             language-description = printable-string



             message-type    = "Delivery Report"
                             / "InterPersonal Notification"
                             / "Multiple Part"



             autosubmitted   = "not-auto-submitted"
                             / "auto-generated"
                             / "auto-replied"
                             / "auto-forwarded"





Kille                                                       [page 150]


RFC 1327bis
MIXER                                                DRAFT Version 2.6



             redirect-comment  = redirect-first *( redirect-subsequent )

             redirect-first = "Originally To:"  mailbox  "Redirected on"
                      date-time "To:"  redirection-reason

             redirect-subsequent = mailbox  "Redirected Again on"
                      date-time "To:"  redirection-reason

             redirection-history-item = "intended recipient" mailbox
                      "redirected to"  redirection-reason
                      "on" date-time


             redirection-reason =
                      "Recipient Assigned Alternate Recipient"
                      / "Originator Requested Alternate Recipient"
                      / "Recipient MD Assigned Alternate Recipient"
                      / "Directory Look Up"
                      / "Alias"


             subject-line  = "Delivery-Report" "(" status ")"
                             [ "for" destination ]

             status        = "success" / "failure" / "success and failures"

             destination   = mailbox / "MTA" word


             extended-heading =
                 "Prevent-NonDelivery-Report" ":"
                 / "Generate-Delivery-Report" ":"
                 / "Alternate-Recipient" ":" prohibition
                 / "Disclose-Recipients" ":"  prohibition
                 / "X400-Content-Return" ":" prohibition











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     Appendix F - Text format for MCGAM distribution



     1.  Text Formats

     This appendix defines text formats for exchange of four types of
     mapping.

     1.   Domain Name Space -> OR Address Space MCGAM

     2.   OR Address Space -> Domain Name Space MCGAM

     3.   Domain Name Space -> OR Address of preferred gateway

     4.   OR Address Space -> Domain Name of preferred gateway


     2.  Mechanisms to register and to distribute MCGAMs

     There is a well known set of MCGAM tables.

     The global coordination of the mapping rules is a part of the
     DANTE MailFLOW Project. New mapping rules may be defined by the
     authority responsible for the relevant name space. The rules need
     to be registered with a national mapping registration authority,
     which in turn passes them on to the central mapping registration
     authority.  All the collected mapping rules are merged together
     into the globally coordinated mapping tables by the MailFLOW
     Project Team. The tables are available from the national mapping
     registration authorities.

     To get a contact address of the mapping registration authority
     for the respective country or more information about the MailFLOW
     Project contact:












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               SWITCH
               MailFLOW Project Team
               Limmatquai 138
               8001 Zuerich
               Switzerland

               email: mailflow@mailflow.dante.net
                      S=MailFLOW;O=MailFLOW;P=DANTE;A=mailnet;C=fi;

               fax:   +41 1 268 15 68
               tel:   +41 1 268 15 20


     3.  Syntax Definitions

     An address syntax is defined, which is compatible with the syntax
     used for 822.domains.  By representing the OR addresses as
     domains, all lookups can be mechanically implemented as domain ->
     domain mappings.  This syntax defined is initially for use in
     table format, but the syntax is defined in a manner which makes
     it suitable to be adapted for  use with the  Domain Name Service.
     This syntax allows for a general representation of OR addresses,
     so that it can be used in other applications.  Not all attributes
     are used in the table formats defined.

          To allow the mapping where a level of the hierarchy is
     omitted, the pseudo-value "@" (not a printable string character)
     is used to indicate omission of a level in the hierarchy.  This
     is distinct from the form including the element with no value,
     although a correct X.400 implementation will interpret both in
     the same manner.

     This syntax is not intended to be handled by users.













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             dmn-or-address  = dmn-part *( "." dmn-part )
             mn-part        = dmn-attribute "$" value
             dmn-attribute  = standard-type
                             /  "~" dmn-printablestring
             value           = dmn-printablestring
                             / "@"
             dmn-printablestring =
                             = *( dmn-char / dmn-pair )
             dmn-char        = <"{", "}", "*", and any ps-char
                                                     except ".">
             dmn-pair        = "\."

     An example usage:

             ~ROLE$Big\.Chief.ADMD$ATT.C$US
             PRMD$DEC.ADMD$@.C$US

     The first example illustrates quoting of a "." and a domain
     define attribute (ROLE).  The second  example illustrates
     omission of the ADMD level. There shall be a strict ordering of
     all components in this table, with the most significant
     components on the RHS.   This allows the encoding to be treated
     as a domain.

          Various further restrictions are placed on the usage of
     dmn-or-address in the address space mapping tables.

     a.   Only C, ADMD, PRMD, O, and up to four OUs may be used.

     b.   No components shall be omitted from this hierarchy, although
          the hierarchy may terminate at any level.  If the mapping is
          to an omitted component, the "@" syntax is used.

     4.  Table Lookups

     When determining a match, there are aspects which apply to all
     lookups.  Matches are always case independent. The key for all
     three  tables is a domain. The longest possible match shall be
     obtained.  Suppose the table has two entries with the following
     keys:

             K.L
             J.K.L



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     Domain "A.B.C" will not return any matches.  Domain "I.J.K.L"
     will match the entry "J.K.L:.

     5.  Domain -> OR Address MCGAM format

     The BNF is:

             domain-syntax "#" dmn-or-address "#"

     EBNF.domain-syntax is defined in Section 4.2. Note that the
     trailing "#" is used for clarity, as the dmn-or-address syntax
     might lead to values with trailing blanks.  Lines starting with
     "#" are comments.

             For example:
             AC.UK#PRMD$UK\.AC.ADMD$GOLD 400.C$GB#
             XEROX.COM#O$Xerox.ADMD$ATT.C$US#
             GMD.DE#O$@.PRMD$GMD.ADMD$DBP.C$DE#

     A domain is looked up to determine the top levels of an OR
     Address.  Components of the domain which are not matched are used
     to build the remainder of the OR address, as described in Section
     4.3.4.

     6.  OR Address -> Domain MCGAM format

     The syntax of this table is:

             dmn-or-address "#" domain-syntax "#"


             For example:

             #
             # Mapping table
             #
             PRMD$UK\.AC.ADMD$GOLD 400.C$GB#AC.UK#

     The OR Address is used to generate a domain key.  It is important
     to order the components correctly, and to fill in missing
     components in the hierarchy.  Use of this mapping is described in
     Section 4.3.2.





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     7.  Domain -> OR Address of Preferred Gateway table

     This uses the same format as the domain -> OR address MCGAM
     table.  In this case, the restriction to only use
     C/ADMD/PRMD/O/OU does not apply.  Use of this mapping is
     described in Section 4.3.4. A domain cannot appear in this table
     and in the domain to OR Address table.

     8.  OR Addresss -> domain of Preferred Gateway table

     This uses the same format as the OR Address -> domain MCGAM
     table.  Use of this mapping is described in Section 4.3.5. An OR
     Address cannot appear in this table and in the OR Address to
     domain table.

































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     Appendix G - Conformance


     This appendix defines a number of options, which a conforming
     gateway shall specify.  Conformance to this specification shall
     not be claimed if any of the mandatory features are not
     implemented.  A specification of conformance may list the service
     elements of Chapter 2, in order to be clear that full conformance
     is provied.  In particular:

     -    Formats for all fields shall be followed.

     -    The gateway shall enable MCGAMs to be used.

     -    Formats for subject lines, delivery reports and IPNs shall
          be followed.   A system which followed the syntax, but
          translated text into a language other than english would be
          conformant.

     -    RFC 1137 shall not be followed when mapping to SMTP.

     -    All mappings of trace shall be implemented.

     -    There shall be a mechanism to access all three global
          mappings.

     -    RFC 1494bis shall be followed for mapping body parts.

     -    When it is specified that a MIME format message is
          generated, RFC 1521 shall be followed.

     A gateway shall specify:

     -    Which Interent Message Transport (822-MTS)  protocols are
          supported.  If SMTP is supported, Appendex A of MIXER shall
          be used.

     -    Which X.400 versions  are supported (84, 88, 92).

     -    Which mechanisms (table, X.500, DNS) are supported to access
          MCGAMs.

     -    The mechanism or mechanisms by which the global mapping
          information is accessed.



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     The following are optional parts of this specification.  A
     conforming implementation shall specify which of these it
     supports.

     -    Support for the extension mappings of Appendix C.

     -    Support for returning illegal format content in a delivery
          report

     -    Which address interpretation heuristics are supported
          (4.3.4.1)

     -    If RFC 987 generated message ids are handled in a backwards
          compatible manner (4.7.3.6)

































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     Appendix H - Change History: RFC 987, 1026, 1138, 1148


     RFC 987 was the original document, and contained the key elements
     of this specification.  It was specific to X.400(1984).  RFC 1026
     specified a small number of necessary changes to RFC 987.

          RFC 1138 was based on the RFC 987 work.  It contained an
     editorial error, and was reissued a few months later as RFC 1148.
     RFC 1148 will be referred to here, as it is the document which is
     widely referred to elsewhere. The major goal of RFC 1148 was to
     upgrade RFC 987 to X.400(1988).  It did this, but did not
     obsolete RFC 987, which was recommended for use with X.400(1984).
     This appendix summarises the changes made in going from RFC 987
     to RFC 1148.

          RFC 1148 noted the following about its upgrade from RFC 987:
     Unnecessary change is usually a bad idea.  Changes on the RFC 822
     side are avoided as far as possible,  so that RFC 822 users do
     not see arbitrary differences between systems conforming to this
     specification, and those following RFC 987.  Changes on the X.400
     side are minimised, but are more  acceptable, due to the mapping
     onto a new set of services and protocols.


     1.  Introduction

     The model has shifted from a protocol based mapping to a service
     based mapping.  This has increased the generality of the
     specification, and improved the model.  This change affects the
     entire document.

          A restriction on scope has been added.

     2.  Service Elements


     -    The new service elements of X.400 are dealt with.

     -    A clear distinction is made between origination and
          reception






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     3.  Basic Mappings


     -    Add teletex support

     -    Add object identifier support

     -    Add labelled integer support

     -    Make PrintableString <-> ASCII mapping reversible

     -    The printable string mapping is aligned to the NBS mapping
          derived from RFC 987.

     4.  Addressing


     -    Support for new addressing attributes

     -    The message ID mapping is changed to not be table driven

     5.  Detailed Mappings


     -    Define extended IPM Header, and use instead of second body
          part for RFC 822 extensions

     -    Realignment of element names

     -    New syntax for reports, simplifying the header and
          introducing a mandatory body format (the RFC 987 header
          format was unusable)

     -    Drop complex autoforwarded mapping

     -    Add full mapping for IP Notifications, defining a body
          format

     -    Adopt an MTS Identifier syntax in line with the OR Address
          syntax

     -    A new format for X400 Trace representation on the RFC 822
          side




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     6.  Appendices


     -    Move Appendix on restricted 822 mappings to a separate RFC

     -    Delete Phonenet and SMTP Appendixes









































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     Appendix I - Change History: RFC 1148 to RFC 1327



     1.  General


     -    The scope of the document was changed to cover X.400(1984),
          and so obsolete RFC 987.

     -    Changes were made to allow usage to connect RFC 822 networks
          using X.400

     -    Text was tightened to be clear about optional and mandatory
          aspects

     -    A good deal of clarification

     -    A number of minor EBNF errors

     -    Better examples are given

     -    Further X.400 upper bounds are handled correctly

     2.  Basic Mappings


     -    The encoding of object identifier is changed slightly

     3.  Addressing


     -    A global mapping of domain to preferred gateway is
          introduced.

     -    An overflow mechanism is defined for RFC 822 addresses of
          greater than 128 bytes

     -    Changes were made to improve compatibility with the PDAM on
          writing OR Addresses.

     +         The PD and Terminal Type keywords were aligned to the
               PDAM.  It is believed that minimal use has been made of
               the RFC 1148 keywords.



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     +         P and A are allowed as alternate keys for PRMD and ADMD

     +         Where keywords are different, the PDAM keywords are
               alternatives on input.  This is mandatory.

     4.  Detailed Mappings


     -    The format of the Subject: lines is defined.

     -    Illegal use (repetition) of the heading EXTENSION is
          corrected, and a new object identifier assigned.

     -    The Delivery Report format is extensively revised in light
          of operational experience.

     -    The handling of redirects is significantly changed, as the
          previous mechanism did not work.

     5.  Appendices


     -    An SMTP appendix is added, allowing optional use of the VRFY
          command to improve probe information.

     -    Handling of JNT Mail Acknowledge-To is changed slightly.

     -    A DDA JNT-MAIL is allowed on input.

     -    The format definitions of Appendix F are explained further,
          and a third table definition added.

     -    An appendix on use with X.400(1984) is added.

     -    Optional extensions are defined to give RFC 822 access to
          further X.400 facilities.

     -    An appendix on conformance is added.









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     Appendix J - Change History: RFC 1327 to this Document



     1.  General

     This update is primarily for stability, and to fold in
     compatibility for MIME and to add support for the new NOTARY
     delivery status notifications.  Other general changes:

     -    Various editorial updates

     -    Minor EBNF errors

     -    Reference to mapping table support by DNS and X.500.

     -    Alignment to X.400(92)

     -    Assignment of a new object identifier

     -    Removal of specification relating to body mapping, which is
          now defined in RFC 1494bis.

     2.  Service Elements


     -    Support of Auto-Submitted service

     3.  Basic Mappings


     -    Comments shall not be used in new headers, to remove parsing
          ambiguity

     -    RFC 1522 encoding may be used as an alternative to X.408
          downgrade, where appropriate.

     -    Correct handling of RFC 822 four year dates.

     4.  Addressing


     -    Replaced the mandatory global address mapping with MCGAMs.




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     -    Add codes and add a heuristic to align to the standard X.400
          form of writing OR Addresses.

     -    Improved text on ordering heuristic

     -    Leading "/" interpretation added

     -    All bar one of the address mapping heuristics made
          mandatory.

     -    Interpretation of domain defined attribute "RFC-822" made
          mandatory in all cases

     -    Make report request comments optional

     5.  Detailed Mappings


     -    Comments no longer maps to separate body part

     -    Allow Languages to be multi-valued

     -    Change Content-Identifier to X400-Content-Identifier, in
          order to avoid confusion with MIME.

     -    Reverse mapping of MIXER defined fields made mandatory

     -    "Expiry-Date:" changed to "Expires:".

     -    "Obsoletes:" changed to "Supersedes:".

     -    Define correct handling when "Resent-Date:" is present.

     6.  Appendices


     -    Change "Content-Return" to "X400-Content-Return" in Appendix
          C.

     -    Relaxation of restrictions on mapping 3 in Appendix F.

     -    Add linkage to HARPOON in Appendix B.

     -    RFC 1494bis added to the conformance statement of Appendix



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          G.

     -    Added Appendix L, with ASN. Summary.












































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          Appendix L - ASN.1 Summary



     MIXER Definitions { iso org(3) dod(6) internet(1) mail(7)
             mixer(1) mixer-core(3) definitions(1) }

     DEFINITIONS IMPLICIT TAGS ::=

     BEGIN

     -- exports everything

     IMPORTS

     EXTENSION FROM
       MTSAbstractService {join-iso-ccit mhs-motis(6) mts(3)
             modules(0) mts-abstract-service(1) }

     HEADING-EXTENSION FROM
       IPMSAbstractService {join-iso-ccit mhs-motis(6) ipms(1)
             modules(0) abstract-service(3) }




     rfc-822-field HEADING-EXTENSION
             VALUE RFC822FieldList
             ::= id-rfc-822-field-list


     RFC822FieldList ::= SEQUENCE OF RFC822Field

     RFC822Field ::= IA5String



     dsn-header-list EXTENSION
        RFC822FieldList
        ::= id-dsn-header-list

     dsn-field-list EXTENSION
        RFC822FieldList
        ::= id-dsn-field-list



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     internet ::= OBJECT IDENTIFIER  { iso org(3) dod(6) 1 } -- from RFC 1155

     mail OBJECT IDENTIFIER ::= { internet 7 }  -- IANA assigned

     mixer OBJECT IDENTIFIER ::= { mail mixer(1) } -- inherited from RFC 1495
     mixer-core OBJECT IDENTIFIER ::= { mixer core(3) }

     id-rfc-822-field-list OBJECT IDENTIFIER ::= {mixer-core 2}
     id-dsn-header-list OBJECT IDENTIFIER ::= {mixer-core 3}
     id-dsn-field-list OBJECT IDENTIFIER ::= {mixer-core 4}

     eit-mixer OBJECT IDENTIFIER ::= {mixer-core 5}
                     -- the MIXER pseudo-EIT



     END -- MIXER ASN.1





























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     SECURITY CONSIDERATIONS

     Security considerations are not discussed in  this RFC.


     AUTHOR'S ADDRESS

     Steve Kille
     Isode Ltd
     The Dome
     The Square
     Richmond
     TW9 1DT
     England

     Phone: +44-181-332-9091

     Internet EMail: S.Kille@ISODE.COM

     X.400 Email: I=S; S=Kille; P=Isode; A=Mailnet; C=FI;

     UFN:  S.Kille, Isode, GB

























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     References


     1.   CCITT , "Recommendations X.400," Message Handling Systems:
          System Model - Service Elements, Oct 1984.

     2.   C. Allocchio, "MaXIM11 - Mapping between X.400 / Internet
          Mail  and Mail-11 mail," RFC 1405bis, Jan 1997.

     3.   C. Allocchio, "Using the Internet DNS to Distribute MIXER
          Conformant Global Address Mapping (MCGAM)," RFC 1664bis, Jan
          1997.

     4.   H.T. Alvestrand, S.E. Kille, R. Miles, M. Rose, and S.
          Thompson, "Mapping between X.400 and RFC-822 Message
          Bodies," RFC 1495, Aug 1993.

     5.   H.T. Alvestrand, J. Romaguera, and K. Jordan, "Rules for
          Downgrading Messages for X.400(88) to X.400(84) When MIME
          Content-Types are Present in the Messages (Harpoon)," RFC
          1496, Aug 1993.

     6.   H.T. Alvestrand and S. Thompson, "Equivalences between X.400
          and RFC-822 Message Bodies," RFC 1494, Aug 1993.

     7.   H.T. Alvestrand, "Tags for the Identification of Languages,"
          RFC 1756, Mar 1995.

     8.   H.T. Alvestrand, "Mapping between X.400 and RFC-822/MIME
          Message Bodies," RFC Draft, Aug 1996.

     9.   N. Borenstein and N. Freed, "MIME (Multipurpose Internet
          Mail Extensions)," RFC 1521, Sep 1993.

     10.  R.T. Braden, "Requirements for Internet Hosts -- Application
          and Support," RFC 1123, Oct 1989.

     11.  CCITT/ISO, "CCITT Recommendations X.420/ ISO/IEC 10021-7,"
          Message Handling Systems: Interpersonal Messaging System,
          Dec 1988.

     12.  CCITT/ISO, "CCITT Recommendations X.411/ ISO/IEC 10021-4,"
          Message Handling Systems: Message Transfer System: Abstract
          Service Definition and Procedures, Dec 1988.



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     13.  CCITT/ISO, "CCITT Recommendations X.400/ ISO/IEC 10021-1,"
          Message Handling: System and Service Overview , Dec 1988.

     14.  CCITT/ISO, "Specification of Abstract Syntax Notation One
          (ASN.1)," CCITT Recommendation X.208 / ISO/IEC 8824, Dec
          1988.

     15.  CCITT/ISO, "CCITT Recommendations X.400/ ISO/IEC 10021-1,"
          Message Handling: System and Service Overview , Dec 1992.

     16.  D.H. Crocker, "Standard of the Format of ARPA Internet Text
          Messages," RFC 822, Aug 1982.

     17.  S.E. Kille, "Mapping Between X.400 and RFC 822," UK Academic
          Community Report (MG.19) / RFC 987, Jun 1986.

     18.  S.E. Kille, "Addendum to RFC 987," UK Academic Community
          Report (MG.23) / RFC 1026, Aug 1987.

     19.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1138, Oct 1989.

     20.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1148, Mar 1990.

     21.  S.E. Kille, "Mapping Between X.400(1988) / ISO 10021 and RFC
          822," RFC 1327, May 1992.

     22.  S.E. Kille, "X.400 1988 to 1984 downgrading," RFC 1328, May
          1992.

     23.  S.E. Kille, "A String Encoding of Presentation Address," RFC
          1278, Nov 1992.

     24.  S.E. Kille, "A String Representation of Distinguished Name,"
          RFC 1485, Jan 1992.

     25.  S.E. Kille, "Using the OSI Directory to achieve User
          Friendly Naming," RFC 1484, Jan 1992.

     26.  S.E. Kille, "Use of an X.500/LDAP directory to support MIXER
          address mapping," RFC 1838bis, Feb 1997.

     27.  N. Koorland, "Message Attachmment Work Group (MAWG): MAWG



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          Feasibility Project Guide," EMA Report, Version 1.5, Nov
          1995.

     28.  K. Moore and G. Vaudreuil, "An Extensible Message Format for
          Delivery Status Notifications," RFC 1894, Jan 1996.

     29.  K. Moore, "SMTP Service Extensions for Delivery Status
          Notifications," RFC 1891, Jan 1996.

     30.  J.B. Postel, "SIMPLE MAIL TRANSFER PROTOCOL," RFC 821, Aug
          1982.




































Kille                                                       [page 172]


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