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Versions: (RFC 1894) 00 01 RFC 3464

     Internet Draft                                          Keith Moore
     Expires in six months                       University of Tennessee
                                                          Greg Vaudreuil
                                                     Lucent Technologies
                                                          April 16, 2002
  
  
          An Extensible Message Format for Delivery Status Notifications
  
                         <draft-vaudreuil-1894bis-01.txt>
  
  
  
  Status of this Memo
  
     This document is an Internet-Draft and is in full conformance with all
     provisions of Section 10 of RFC 2026.
  
     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 valid for a maximum of six months and may be updated,
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     inappropriate to use Internet Drafts as reference material or to cite
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  Copyright Notice
  
     Copyright (C) The Internet Society (2002). All Rights Reserved.
  
     This Internet-Draft is in conformance with Section 10 of RFC 2026.
  

  
  
     Internet Draft    Delivery Status Notifications      April 16, 2002
  
  
  Abstract
  
     This memo defines a MIME content-type that may be used by a message
     transfer agent (MTA) or electronic mail gateway to report the result of
     an attempt to deliver a message to one or more recipients. This content-
     type is intended as a machine-processable replacement for the various
     types of delivery status notifications currently used in Internet
     electronic mail.
  
     Because many messages are sent between the Internet and other messaging
     systems (such as X.400 or the so-called "LAN-based" systems), the DSN
     protocol is designed to be useful in a multi- protocol messaging
     environment. To this end, the protocol described in this memo provides
     for the carriage of "foreign" addresses and error codes, in addition to
     those normally used in Internet mail. Additional attributes may also be
     defined to support "tunneling" of foreign notifications through Internet
     mail.
  
  
  Working Group Summary
  
     RFC 1894 was a product of the Notary working group. This document is a
     revision of that document providing clarifications as necessary to
     advance to draft standard.
  
     Any questions, comments, and reports of defects or ambiguities in this
     specification may be sent to the mailing list for the NOTARY working
     group of the IETF, using the address <notifications@cs.utk.edu>. Requests
     to subscribe to the mailing list should be addressed to <notifications-
     request@cs.utk.edu>. Implementers of this specification are encouraged to
     subscribe to the mailing list, so that they will quickly be informed of
     any problems which might hinder interoperability.
  
  Document Conventions
  
     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
     "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
     document are to be interpreted as described in RFC-2119 [RFC2119].
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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     Internet Draft    Delivery Status Notifications      April 16, 2002
  
  
  Table of Contents
  
  1. INTRODUCTION ........................................................4
    1.1 Purposes .........................................................4
    1.2 Requirements .....................................................5
    1.3 Terminology ......................................................5
  2. FORMAT OF A DELIVERY STATUS NOTIFICATION ............................8
    2.1 The message/delivery-status content-type .........................9
     2.1.1 General conventions for DSN fields ............................9
     2.1.2 "*-type" sub-fields ...........................................9
     2.1.3 Lexical tokens imported from RFC 822 .........................10
    2.2 Per-Message DSN Fields ..........................................10
     2.2.1 The Original-Envelope-Id field ...............................11
     2.2.2 The Reporting-MTA DSN field ..................................11
     2.2.3 The DSN-Gateway field ........................................12
     2.2.4 The Received-From-MTA DSN field ..............................13
     2.2.5 The Arrival-Date DSN field ...................................13
    2.3 Per-Recipient DSN fields ........................................13
     2.3.1 Original-Recipient field .....................................14
     2.3.2 Final-Recipient field ........................................14
     2.3.3 Action field .................................................15
     2.3.4 Status field .................................................16
     2.3.5 Remote-MTA field .............................................17
     2.3.6 Diagnostic-Code field ........................................17
     2.3.7 Last-Attempt-Date field ......................................18
     2.3.8 final-log-id field ...........................................18
     2.3.9 Will-Retry-Until field .......................................18
  3. CONFORMANCE AND USAGE REQUIREMENTS .................................20
  4. SECURITY CONSIDERATIONS ............................................21
    4.1 Forgery .........................................................21
    4.2 Confidentiality .................................................21
    4.3 Non-Repudiation .................................................22
  5. REFERENCES .........................................................23
  7. ACKNOWLEDGMENTS ....................................................25
  8. AUTHOR'S ADDRESS ...................................................25
  APPENDIX A - COLLECTED GRAMMAR ........................................26
  APPENDIX B - GUIDELINES FOR GATEWAYING DSNS ...........................28
    Gatewaying from other mail systems to DSNs ..........................28
    Gatewaying from DSNs to other mail systems ..........................28
  APPENDIX C - GUIDELINES FOR USE OF DSNS BY MAILING LIST EXPLODERS .....30
  APPENDIX D - IANA REGISTRATION FORMS FOR DSN TYPES ....................31
    IANA registration form for address-type .............................31
    IANA registration form for diagnostic-type ..........................31
    IANA registration form for MTA-name-type ............................31
  APPENDIX E - EXAMPLES .................................................33
    Simple DSN ..........................................................34
    Multi-Recipient DSN .................................................35
    DSN from gateway to foreign system ..................................36
    Delayed DSN .........................................................37
  APPENDIX F - CHANGES FROM RFC1894 .....................................38
  
  
  
  
  
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  1. Introduction
  
     This memo defines a MIME [MIME1] content-type for delivery status
     notifications (DSNs). A DSN can be used to notify the sender of a message
     of any of several conditions: failed delivery, delayed delivery,
     successful delivery, or the gatewaying of a message into an environment
     that may not support DSNs. The "message/delivery-status" content-type
     defined herein is intended for use within the framework of the
     "multipart/report" content type defined in [REPORT].
  
     This memo defines only the format of the notifications. An extension to
     the Simple Message Transfer Protocol (SMTP)[SMTP] to fully support such
     notifications is the subject of a separate memo [DRPT].
  
  1.1 Purposes
  
     The DSNs defined in this memo are expected to serve several purposes:
  
     (a) Inform human beings of the status of message delivery processing, as
        well as the reasons for any delivery problems or outright failures,
        in a manner that is largely independent of human language and media;
  
     (b) Allow mail user agents to keep track of the delivery status of
        messages sent, by associating returned DSNs with earlier message
        transmissions;
  
     (c) Allow mailing list exploders to automatically maintain their
        subscriber lists when delivery attempts repeatedly fail;
  
     (d) Convey delivery and non-delivery notifications resulting from
        attempts to deliver messages to "foreign" mail systems via a gateway;
  
     (e) Allow "foreign" notifications to be tunneled through a MIME-capable
        message system and back into the original messaging system that
        issued the original notification, or even to a third messaging
        system;
  
     (f) Allow language-independent and medium-independent, yet reasonably
        precise, indications of the reason for the failure of a message to be
        delivered; and
  
     (g) Provide sufficient information to remote MTA maintainers (via
        "trouble tickets") so that they can understand the nature of reported
        errors. This feature is used in the case that failure to deliver a
        message is due to the malfunction of a remote MTA and the sender
        wants to report the problem to the remote MTA administrator.
  
  
  
  
  
  
  
  
  
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  1.2 Requirements
  
     These purposes place the following constraints on the notification
     protocol:
  
     (a) It must be readable by humans as well as being machine-parsable.
  
     (b) It must provide enough information to allow message senders (or the
     user agents) to unambiguously associate a DSN with the message that was
     sent and the original recipient address for which the DSN is issued (if
     such information is available), even if the message was forwarded to
     another recipient address.
  
     (c) It must be able to preserve the reason for the success or failure of
     a delivery attempt in a remote messaging system, using the "language"
     (mailbox addresses and status codes) of that remote system.
  
     (d) It must also be able to describe the reason for the success or
     failure of a delivery attempt, independent of any particular human
     language or of the "language" of any particular mail system.
  
     (e) It must preserve enough information to allow the maintainer of a
     remote MTA to understand (and if possible, reproduce) the conditions that
     caused a delivery failure at that MTA.
  
     (f) For any notifications issued by foreign mail systems, which are
     translated by a mail gateway to the DSN format, the DSN must preserve the
     "type" of the foreign addresses and error codes, so that these may be
     correctly interpreted by gateways.
  
     A DSN contains a set of per-message fields that identify the message and
     the transaction during which the message was submitted, along with other
     fields that apply to all delivery attempts described by the DSN. The DSN
     also includes a set of per-recipient fields to convey the result of the
     attempt to deliver the message to each of one or more recipients.
  
  1.3 Terminology
  
     A message may be transmitted through several message transfer agents
     (MTAs) on its way to a recipient. For a variety of reasons, recipient
     addresses may be rewritten during this process, so each MTA may
     potentially see a different recipient address. Depending on the purpose
     for which a DSN is used, different formats of a particular recipient
     address will be needed.
  
     Several DSN fields are defined in terms of the view from a particular MTA
     in the transmission. The MTAs are assigned the following names:
  
     (a) Original MTA
  
         The Original MTA is the one to which the message is submitted for
         delivery by the sender of the message.
  
     (b) Reporting MTA
  
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         For any DSN, the Reporting MTA is the one which is reporting the
         results of delivery attempts described in the DSN.
  
         If the delivery attempts described occurred in a "foreign" (non-
         Internet) mail system, and the DSN was produced by translating the
         foreign notice into DSN format, the Reporting MTA will still
         identify the "foreign" MTA where the delivery attempts occurred.
  
     (c) Received-From MTA
  
         The Received-From MTA is the MTA from which the Reporting MTA
         received the message, and accepted responsibility for delivery of
         the message.
  
     (d) Remote MTA
  
         If an MTA determines that it must relay a message to one or more
         recipients, but the message cannot be transferred to its "next hop"
         MTA, or if the "next hop" MTA refuses to accept responsibility for
         delivery of the message to one or more of its intended recipients,
         the relaying MTA may need to issue a DSN on behalf of the recipients
         for whom the message cannot be delivered. In this case the relaying
         MTA is the Reporting MTA, and the "next hop" MTA is known as the
         Remote MTA.
  
     Figure 1 illustrates the relationship between the various MTAs.
  
  
  
     +-----+    +--------+           +---------+    +---------+      +------+
     |     |    |        |           |Received-|    |         |      |      |
     |     | => |Original| => ... => |  From   | => |Reporting| ===> |Remote|
     | user|    |   MTA  |           |   MTA   |    |   MTA   | <No! |  MTA |
     |agent|    +--------+           +---------+    +----v----+      +------+
     |     |                                             |
     |     | <-------------------------------------------+
     +-----+      (DSN returned to sender by Reporting MTA)
  
      Figure 1. Original, Received-From, Reporting and Remote MTAs
  
  
  
     Each of these MTAs may provide information that is useful in a DSN:
  
     + Ideally, the DSN will contain the address of each recipient as
      originally specified to the Original MTA by the sender of the message.
  
      This version of the address is needed (rather than a forwarding address
      or some modified version of the original address) so that the sender
      may compare the recipient address in the DSN with the address in the
      sender's records (e.g. an address book for an individual, the list of
      subscribers for a mailing list) and take appropriate action.
  
  
  
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      Similarly, the DSN might contain an "envelope identifier" that was
      known to both the sender's user agent and the Original MTA at the time
      of message submission, and which, if included in the DSN, can be used
      by the sender to keep track of which messages were or were not
      delivered.
  
     + If a message was (a) forwarded to a different address than that
      specified by the sender, (b) gatewayed to a different mail system than
      that used by the sender, or (c) subjected to address rewriting during
      transmission, the "final" form of the recipient address (i.e. the one
      seen by the Reporting MTA) will be different than the original (sender-
      specified) recipient address. Just as the sender's user agent (or the
      sender) prefers the original recipient address, so the "final" address
      is needed when reporting a problem to the postmaster of the site where
      message delivery failed, because only the final recipient address will
      allow her to reproduce the conditions that caused the failure.
  
     + A "failed" DSN should contain the most accurate explanation for the
      delivery failure that is available. For ease of interpretation, this
      information should be a format that is independent of the mail
      transport system that issued the DSN. However, if a foreign error code
      is translated into some transport-independent format, some information
      may be lost. It is therefore desirable to provide both a transport-
      independent status code and a mechanism for reporting transport-
      specific codes. Depending on the circumstances that produced delivery
      failure, the transport-specific code might be obtained from either the
      Reporting MTA or the Remote MTA.
  
     Since different values for "recipient address" and "delivery status code"
     are needed according to the circumstance in which a DSN will be used, and
     since the MTA that issues the DSN cannot anticipate those circumstances,
     the DSN format described here may contain both the original and final
     forms of a recipient address, and both a transport-independent and a
     transport-specific indication of delivery status.
  
     Extension fields may also be added by the Reporting MTA as needed to
     provide additional information for use in a trouble ticket or to preserve
     information for tunneling of foreign delivery reports through Internet
     DSNs.
  
     The Original, Reporting, and Remote MTAs may exist in very different
     environments and use dissimilar transport protocols, MTA names, address
     formats, and delivery status codes. DSNs therefore do not assume any
     particular format for mailbox addresses, MTA names, or transport-specific
     status codes. Instead, the various DSN fields that carry such quantities
     consist of a "type" sub-field followed by a sub-field whose contents are
     ordinary text characters, and the format of which is indicated by the
     "type" sub-field. This allows a DSN to convey these quantities regardless
     of format.
  
  
  
  
  
  
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  2. Format of a Delivery Status Notification
  
     A DSN is a MIME message with a top-level content-type of multipart/report
     (defined in [REPORT]). When a multipart/report content is used to
     transmit a DSN:
  
     (a) The report-type parameter of the multipart/report content is
        "delivery-status".
  
     (b) The first component of the multipart/report contains a human-
        readable explanation of the DSN, as described in [REPORT].
  
     (c) The second component of the multipart/report is of content-type
        message/delivery-status, described in section 2.1 of this document.
  
     (d) If the original message or a portion of the message is to be returned
        to the sender, it appears as the third component of the
        multipart/report.
  
     NOTE: For delivery status notifications gatewayed from foreign systems,
     the headers of the original message may not be available. In this case
     the third component of the DSN may be omitted, or it may contain
     "simulated" RFC 822 headers that contain equivalent information. In
     particular, it is very desirable to preserve the subject, date, and
     message-id (or equivalent) fields from the original message.
  
     The DSN MUST be addressed (in both the message header and the transport
     envelope) to the return address from the transport envelope which
     accompanied the original message for which the DSN was generated. (For a
     message that arrived via SMTP, the envelope return address appears in the
     MAIL FROM command.)
  
     The From field of the message header of the DSN SHOULD contain the
     address of a human who is responsible for maintaining the mail system at
     the Reporting MTA site (e.g. Postmaster), so that a reply to the DSN will
     reach that person. Exception: if a DSN is translated from a foreign
     delivery report, and the gateway performing the translation cannot
     determine the appropriate address, the From field of the DSN MAY be the
     address of a human who is responsible for maintaining the gateway.
  
     The envelope sender address of the DSN SHOULD be chosen to ensure that no
     delivery status reports will be issued in response to the DSN itself, and
     MUST be chosen so that DSNs will not generate mail loops. Whenever an
     SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a
     NULL return address, i.e. "MAIL FROM:<>".
  
     A particular DSN describes the delivery status for exactly one message.
     However, an MTA MAY report on the delivery status for several recipients
     of the same message in a single DSN. Due to the nature of the mail
     transport system (where responsibility for delivery of a message to its
     recipients may be split among several MTAs, and delivery to any
     particular recipient may be delayed), multiple DSNs may be still be
     issued in response to a single message submission.
  
  
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  2.1 The message/delivery-status content-type
  
     The message/delivery-status content-type is defined as follows:
  
     MIME type name:             message
     MIME subtype name:          delivery-status
     Optional parameters:        none
     Encoding considerations:    "7bit" encoding is sufficient and MUST be
                                 used to maintain readability when viewed by
                                 non-MIME mail readers.
     Security considerations:    discussed in section 4 of this memo.
  
     The message/delivery-status report type for use in the multipart/report
     is "delivery-status".
  
     The body of a message/delivery-status consists of one or more "fields"
     formatted according to the ABNF of RFC 822 header "fields" (see
     [RFC822]). The per-message fields appear first, followed by a blank line.
     Following the per-message fields are one or more groups of per-recipient
     fields. Each group of per-recipient fields is preceded by a blank line.
     Using the ABNF of RFC 822, the syntax of the message/delivery-status
     content is as follows:
  
                delivery-status-content =  per-message-fields 1*
                                          ( CRLF per-recipient-fields )
  
     The per-message fields are described in section 2.2. The per- recipient
     fields are described in section 2.3.
  
  2.1.1 General conventions for DSN fields
  
     Since these fields are defined according to the rules of RFC 822, the
     same conventions for continuation lines and comments apply. Notification
     fields may be continued onto multiple lines by beginning each additional
     line with a SPACE or HTAB. Text that appears in parentheses is considered
     a comment and not part of the contents of that notification field. Field
     names are case-insensitive, so the names of notification fields may be
     spelled in any combination of upper and lower case letters. Comments in
     DSN fields may use the "encoded-word" construct defined in [MIME3].
  
  2.1.2 "*-type" sub-fields
  
     Several DSN fields consist of a "-type" sub-field, followed by a
     semicolon, followed by "*text". For these fields, the keyword used in the
     address-type, diagnostic-type, or MTA-name-type sub-field indicates the
     expected format of the address, status-code, or MTA- name which follows.
  
     The "-type" sub-fields are defined as follows:
  
     (a) An "address-type" specifies the format of a mailbox address. For
         example, Internet mail addresses use the "rfc822" address-type.
  
                 address-type = atom
  
  
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     (b) A "diagnostic-type" specifies the format of a status code. For
         example, when a DSN field contains a reply code reported via the
         Simple Mail Transfer Protocol [SMTP], the "smtp" diagnostic-type is
         used.
  
                 diagnostic-type = atom
  
     (c) An "MTA-name-type" specifies the format of an MTA name. For example,
         for an SMTP server on an Internet host, the MTA name is the domain
         name of that host, and the "dns" MTA-name-type is used.
  
                 mta-name-type = atom
  
     Values for address-type, diagnostic-type, and MTA-name-type are case-
     insensitive. Thus address-type values of "RFC822" and "rfc822" are
     equivalent.
  
     The Internet Assigned Numbers Authority (IANA) will maintain a registry
     of address-types, diagnostic-types, and MTA-name-types, along with
     descriptions of the meanings and acceptable values of each, or a
     reference to one or more specifications that provide such descriptions.
     (The "rfc822" address-type, "smtp" diagnostic- type, and "dns" MTA-name-
     type are defined in [DRPT].) Registration forms for address-type,
     diagnostic-type, and MTA-name-type appear in Appendix D.
  
     IANA will not accept registrations for any address-type, diagnostic-
     type, or MTA-name-type name that begins with "X-". These type names are
     reserved for experimental use.
  
  2.1.3 Lexical tokens imported from RFC 822
  
     The following lexical tokens, defined in [RFC822], are used in the ABNF
     grammar for DSNs: atom, CHAR, comment, CR, CRLF, DIGIT, LF, linear-
     white-space, SPACE, text. The date-time lexical token is defined in
     [HOSTREQ].
  
  2.2 Per-Message DSN Fields
  
     Some fields of a DSN apply to all of the delivery attempts described by
     that DSN. These fields may appear at most once in any DSN. These fields
     are used to correlate the DSN with the original message transaction and
     to provide additional information which may be useful to gateways.
  
            per-message-fields =
                  [ original-envelope-id-field CRLF ]
                  reporting-mta-field CRLF
                  [ dsn-gateway-field CRLF ]
                  [ received-from-mta-field CRLF ]
                  [ arrival-date-field CRLF ]
                  *( extension-field CRLF )
  
  
  
  
  
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  2.2.1 The Original-Envelope-Id field
  
     The optional Original-Envelope-Id field contains an "envelope identifier"
     that uniquely identifies the transaction during which the message was
     submitted, and was either (a) specified by the sender and supplied to the
     sender's MTA, or (b) generated by the sender's MTA and made available to
     the sender when the message was submitted. Its purpose is to allow the
     sender (or her user agent) to associate the returned DSN with the
     specific transaction in which the message was sent.
  
     If such an envelope identifier was present in the envelope that
     accompanied the message when it arrived at the Reporting MTA, it SHOULD
     be supplied in the Original-Envelope-Id field of any DSNs issued as a
     result of an attempt to deliver the message. Except when a DSN is issued
     by the sender's MTA, an MTA MUST NOT supply this field unless there is an
     envelope-identifier field in the envelope that accompanied this message
     on its arrival at the Reporting MTA.
  
     The Original-Envelope-Id field is defined as follows:
  
             original-envelope-id-field =
                    "Original-Envelope-Id" ":" envelope-id
  
              envelope-id = *text
  
     There may be at most one Original-Envelope-Id field per DSN.
  
     The envelope-id is CASE-SENSITIVE. The DSN MUST preserve the original
     case and spelling of the envelope-id.
  
             NOTE: The Original-Envelope-Id is NOT the same as the Message-Id
             from the message header. The Message-Id identifies the content of
             the message, while the Original-Envelope-Id identifies the
             transaction in which the message is sent.
  
  2.2.2 The Reporting-MTA DSN field
  
           reporting-mta-field =
                 "Reporting-MTA" ":" mta-name-type ";" mta-name
  
            mta-name = *text
  
     The Reporting-MTA field is defined as follows:
  
     A DSN describes the results of attempts to deliver, relay, or gateway a
     message to one or more recipients. In all cases, the Reporting-MTA is the
     MTA that attempted to perform the delivery, relay, or gateway operation
     described in the DSN. This field is required.
  
     Note that if an SMTP client attempts to relay a message to an SMTP server
     and receives an error reply to a RCPT command, the client is responsible
     for generating the DSN, and the client's domain name will appear in the
     Reporting-MTA field. (The server's domain name will appear in the Remote-
     MTA field.)
  
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     Note that the Reporting-MTA is not necessarily the MTA which actually
     issued the DSN. For example, if an attempt to deliver a message outside
     of the Internet resulted in a non-delivery notification which was
     gatewayed back into Internet mail, the Reporting-MTA field of the
     resulting DSN would be that of the MTA that originally reported the
     delivery failure, not that of the gateway which converted the foreign
     notification into a DSN. See Figure 2.
  
     sender's environment                            recipient's environment
     ............................ ..........................................
                                : :
                            (1) : :                             (2)
       +-----+  +--------+  +--------+  +---------+  +---------+   +------+
       |     |  |        |  |        |  |Received-|  |         |   |      |
       |     |=>|Original|=>|        |->|  From   |->|Reporting|-->|Remote|
       | user|  |   MTA  |  |        |  |   MTA   |  |   MTA   |<No|  MTA |
       |agent|  +--------+  |Gateway |  +---------+  +----v----+   +------+
       |     |              |        |                    |
       |     | <============|        |<-------------------+
       +-----+              |        |(4)                (3)
                            +--------+
                                : :
     ...........................: :.........................................
  
                    Figure 2. DSNs in the presence of gateways
  
      (1) message is gatewayed into recipient's environment
      (2) attempt to relay message fails
      (3) reporting-mta (in recipient's environment) returns non-delivery
           notification
      (4) gateway translates foreign notification into a DSN
  
     The mta-name portion of the Reporting-MTA field is formatted according to
     the conventions indicated by the mta-name-type sub-field. If an MTA
     functions as a gateway between dissimilar mail environments and thus is
     known by multiple names depending on the environment, the mta-name sub-
     field SHOULD contain the name used by the environment from which the
     message was accepted by the Reporting-MTA.
  
     Because the exact spelling of an MTA name may be significant in a
     particular environment, MTA names are CASE-SENSITIVE.
  
  2.2.3 The DSN-Gateway field
  
     The DSN-Gateway field indicates the name of the gateway or MTA that
     translated a foreign (non-Internet) delivery status notification into
     this DSN. This field MUST appear in any DSN that was translated by a
     gateway from a foreign system into DSN format, and MUST NOT appear
     otherwise.
  
          dsn-gateway field = "DSN
  
     For gateways into Internet mail, the MTA-name-type will normally be
     "dns", and the mta-name will be the Internet domain name of the gateway.
  
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  2.2.4 The Received-From-MTA DSN field
  
     The optional Received-From-MTA field indicates the name of the MTA from
     which the message was received.
  
          received-from-mta-field =
               "Received-From-MTA" ":" mta-name-type ";" mta-name
  
     If the message was received from an Internet host via SMTP, the contents
     of the mta-name sub-field SHOULD be the Internet domain name supplied in
     the HELO or EHLO command, and the network address used by the SMTP client
     SHOULD be included as a comment enclosed in parentheses. (In this case,
     the MTA-name-type will be "dns".)
  
     The mta-name portion of the Received-From-MTA field is formatted
     according to the conventions indicated by the MTA-name-type sub-field.
  
     Since case is significant in some mail systems, the exact spelling,
     including case, of the MTA name SHOULD be preserved.
  
  2.2.5 The Arrival-Date DSN field
  
     The optional Arrival-Date field indicates the date and time at which the
     message arrived at the Reporting MTA. If the Last-Attempt-Date field is
     also provided in a per-recipient field, this can be used to determine the
     interval between when the message arrived at the Reporting MTA and when
     the report was issued for that recipient.
  
          arrival-date-field = "Arrival-Date" ":" date-time
  
     The date and time are expressed in RFC 822 'date-time' format, as
     modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
  
  2.3 Per-Recipient DSN fields
  
     A DSN contains information about attempts to deliver a message to one or
     more recipients. The delivery information for any particular recipient is
     contained in a group of contiguous per-recipient fields. Each group of
     per-recipient fields is preceded by a blank line.
  
     The syntax for the group of per-recipient fields is as follows:
  
          per-recipient-fields =
                [ original-recipient-field CRLF ]
                final-recipient-field CRLF
                action-field CRLF
                status-field CRLF
                [ remote-mta-field CRLF ]
                [ diagnostic-code-field CRLF ]
                [ last-attempt-date-field CRLF ]
                [ final-log-id CRLF ]
                [ will-retry-until-field CRLF ]
                *( extension-field CRLF )
  
  
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  2.3.1 Original-Recipient field
  
     The Original-Recipient field indicates the original recipient address as
     specified by the sender of the message for which the DSN is being issued.
  
         original-recipient-field =
               "Original-Recipient" ":" address-type ";" generic-address
  
          generic-address = *text
  
     The address-type field indicates the type of the original recipient
     address. If the message originated within the Internet, the address-type
     field will normally be "rfc822", and the address will be according to the
     syntax specified in [RFC822]. The value "unknown" should be used if the
     Reporting MTA cannot determine the type of the original recipient address
     from the message envelope.
  
     This field is optional. It should be included only if the sender-
     specified recipient address was present in the message envelope, such as
     by the SMTP extensions defined in [DRPT]. This address is the same as
     that provided by the sender and can be used to automatically correlate
     DSN reports and message transactions.
  
  2.3.2 Final-Recipient field
  
     The Final-Recipient field indicates the recipient for which this set of
     per-recipient fields applies. This field MUST be present in each set of
     per-recipient data.
  
     The syntax of the field is as follows:
  
           final-recipient-field =
               "Final-Recipient" ":" address-type ";" generic-address
  
     The generic-address sub-field of the Final-Recipient field MUST contain
     the mailbox address of the recipient (from the transport envelope), as it
     was when the Reporting MTA accepted the message for delivery.
  
     The Final-Recipient address may differ from the address originally
     provided by the sender, because it may have been transformed during
     forwarding and gatewaying into an totally unrecognizable mess. However,
     in the absence of the optional Original-Recipient field, the Final-
     Recipient field and any returned content may be the only information
     available with which to correlate the DSN with a particular message
     submission.
  
     The address-type sub-field indicates the type of address expected by the
     reporting MTA in that context. Recipient addresses obtained via SMTP will
     normally be of address-type "rfc822".
  
     NOTE: The Reporting MTA is not expected to ensure that the address
     actually conforms to the syntax conventions of the address-type. Instead,
     it MUST report exactly the address received in the envelope, unless that
  
  
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     address contains characters such as CR or LF which are not allowed in a
     DSN field.
  
     Since mailbox addresses (including those used in the Internet) may be
     case sensitive, the case of alphabetic characters in the address MUST be
     preserved.
  
  2.3.3 Action field
  
     The Action field indicates the action performed by the Reporting-MTA as a
     result of its attempt to deliver the message to this recipient address.
     This field MUST be present for each recipient named in the DSN.
  
     The syntax for the action-field is:
  
          action-field = "Action" ":" action-value
  
          action-value =
                "failed" / "delayed" / "delivered" / "relayed" / "expanded"
  
     The action-value may be spelled in any combination of upper and lower
     case characters.
  
     "failed"   indicates that the message could not be delivered to the
                recipient. The Reporting MTA has abandoned any attempts to
                deliver the message to this recipient. No further
                notifications should be expected.
  
     "delayed"  indicates that the Reporting MTA has so far been unable to
                deliver or relay the message, but it will continue to
                attempt to do so. Additional notification messages may be
                issued as the message is further delayed or successfully
                delivered, or if delivery attempts are later abandoned.
  
     "delivered" indicates that the message was successfully delivered to
                the recipient address specified by the sender, which
                includes "delivery" to a mailing list exploder. It does
                not indicate that the message has been read. This is a
                terminal state and no further DSN for this recipient should
                be expected.
  
     "relayed"  indicates that the message has been relayed or gatewayed
                into an environment that does not accept responsibility for
                generating DSNs upon successful delivery. This action-
                value SHOULD NOT be used unless the sender has requested
                notification of successful delivery for this recipient.
  
     "expanded"  indicates that the message has been successfully delivered
                to the recipient address as specified by the sender, and
                forwarded by the Reporting-MTA beyond that destination to
                multiple additional recipient addresses. An action-value
                of "expanded" differs from "delivered" in that "expanded"
                is not a terminal state. Further "failed" and/or "delayed"
                notifications may be provided.
  
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     Using the terms "mailing list" and "alias" as defined in      [DRPT],
     section 7.2.7: An action-value of "expanded" is only      to be used when
     the message is delivered to a multiple-      recipient "alias". An
     action-value of "expanded" SHOULD      NOT be used with a DSN issued on
     delivery of a message to a "mailing list".
  
            NOTE ON ACTION VS. STATUS CODES: Although the 'action' field
            might seem to be redundant with the 'status' field, this is not
            the case. In particular, a "temporary failure" ("4") status code
            could be used with an action-value of either "delayed" or
            "failed". For example, assume that an SMTP client repeatedly
            tries to relay a message to the mail exchanger for a recipient,
            but fails because a query to a domain name server timed out.
            After a few hours, it might issue a "delayed" DSN to inform the
            sender that the message had not yet been delivered. After a few
            days, the MTA might abandon its attempt to deliver the message
            and return a "failed" DSN. The status code (which would begin
            with a "4" to indicate "temporary failure") would be the same for
            both DSNs.
  
            Another example for which the action and status codes may appear
            contradictory: If an MTA or mail gateway cannot deliver a message
            because doing so would entail conversions resulting in an
            unacceptable loss of information, it would issue a DSN with the
            'action' field of "failure" and a status code of 'XXX'. If the
            message had instead been relayed, but with some loss of
            information, it might generate a DSN with the same XXX status-
            code, but with an action field of "relayed".
  
  2.3.4 Status field
  
     The per-recipient Status field contains a transport-independent status
     code that indicates the delivery status of the message to that recipient.
     This field MUST be present for each delivery attempt which is described
     by a DSN.
  
     The syntax of the status field is:
  
          status-field = "Status" ":" status-code
  
          status-code = DIGIT "." 1*3DIGIT "." 1*3DIGIT
  
             ; White-space characters and comments are NOT allowed within
             ; a status-code, though a comment enclosed in parentheses MAY
             ; follow the last numeric sub-field of the status-code. Each
             ; numeric sub-field within the status-code MUST be expressed
             ; without leading zero digits.
  
     Status codes thus consist of three numerical fields separated by ".". The
     first sub-field indicates whether the delivery attempt was successful (2
     = success, 4 = persistent temporary failure, 5 = permanent failure). The
     second sub-field indicates the probable source of any delivery anomalies,
     and the third sub-field denotes a precise error condition, if known.
  
  
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     The initial set of status-codes is defined in [STATUS].
  
  2.3.5 Remote-MTA field
  
     The value associated with the Remote-MTA DSN field is a printable ASCII
     representation of the name of the "remote" MTA that reported delivery
     status to the "reporting" MTA.
  
          remote-mta field = "Remote
  
     NOTE: The Remote-MTA field preserves the "while talking to" information
     that was provided in some pre-existing nondelivery reports.
  
     This field is optional. It MUST NOT be included if no remote MTA was
     involved in the attempted delivery of the message to that recipient.
  
  2.3.6 Diagnostic-Code field
  
     For a "failed" or "delayed" recipient, the Diagnostic-Code DSN field
     contains the actual diagnostic code issued by the mail transport. Since
     such codes vary from one mail transport to another, the diagnostic-type
     sub-field is needed to specify which type of diagnostic code is
     represented.
  
          diagnostic-code-field =
                "Diagnostic-Code" ":" diagnostic-type ";" *text
  
          NOTE: The information in the Diagnostic-Code field may be somewhat
          redundant with that from the Status field. The Status field is
          needed so that any DSN, regardless of origin, may be understood by
          any user agent or gateway that parses DSNs. Since the Status code
          will sometimes be less precise than the actual transport diagnostic
          code, the Diagnostic-Code field is provided to retain the latter
          information. Such information may be useful in a trouble ticket sent
          to the administrator of the Reporting MTA, or when tunneling foreign
          non-delivery reports through DSNs.
  
     If the Diagnostic Code was obtained from a Remote MTA during an attempt
     to relay the message to that MTA, the Remote-MTA field should be present.
     When interpreting a DSN, the presence of a Remote-MTA field indicates
     that the Diagnostic Code was issued by the Remote MTA. The absence of a
     Remote-MTA indicates that the Diagnostic Code was issued by the Reporting
     MTA.
  
     In addition to the Diagnostic-Code itself, additional textual description
     of the diagnostic, MAY appear in a comment enclosed in parentheses.
  
     This field is optional, because some mail systems supply no additional
     information beyond that which is returned in the 'action' and 'status'
     fields. However, this field SHOULD be included if transport-specific
     diagnostic information is available.
  
  
  
  
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  2.3.7 Last-Attempt-Date field
  
     The Last-Attempt-Date field gives the date and time of the last attempt
     to relay, gateway, or deliver the message (whether successful or
     unsuccessful) by the Reporting MTA. This is not necessarily the same as
     the value of the Date field from the header of the message used to
     transmit this delivery status notification: In cases where the DSN was
     generated by a gateway, the Date field in the message header contains the
     time the DSN was sent by the gateway and the DSN Last-Attempt-Date field
     contains the time the last delivery attempt occurred.
  
          last-attempt-date-field = "Last-Attempt-Date" ":" date-time
  
     This field is optional. It MUST NOT be included if the actual date and
     time of the last delivery attempt are not available (which might be the
     case if the DSN were being issued by a gateway).
  
     The date and time are expressed in RFC 822 'date-time' format, as
     modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
  
  2.3.8 final-log-id field
  
     The "final-log-id" field gives the final-log-id of the message that was
     used by the final-mta. This can be useful as an index to the final-mta's
     log entry for that delivery attempt.
  
          final-log-id-field = "Final-Log-ID" ":" *text
  
     This field is optional.
  
  2.3.9 Will-Retry-Until field
  
     For DSNs of type "delayed", the Will-Retry-Until field gives the date
     after which the Reporting MTA expects to abandon all attempts to deliver
     the message to that recipient. The Will-Retry-Until field is optional for
     "delay" DSNs, and MUST NOT appear in other DSNs.
  
          will-retry-until-field = "Will-Retry-Until" ":" date-time
  
     The date and time are expressed in RFC 822 'date-time' format, as
     modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
  
     2.4 Extension fields
  
     Additional per-message or per-recipient DSN fields may be defined in the
     future by later revisions or extensions to this specification. Extension-
     field names beginning with "X-" will never be defined as standard fields;
     such names are reserved for experimental use. DSN field names NOT
     beginning with "X-" MUST be registered with the Internet Assigned Numbers
     Authority (IANA) and published in an RFC.
  
  
  
  
  
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     Extension DSN fields may be defined for the following reasons:
  
     (a) To allow additional information from foreign delivery status
         reports to be tunneled through Internet DSNs. The names of such
         DSN fields should begin with an indication of the foreign
         environment name (e.g. X400-Physical-Forwarding-Address).
  
     (b) To allow the transmission of diagnostic information which is
         specific to a particular mail transport protocol. The names of
         such DSN fields should begin with an indication of the mail
         transport being used (e.g. SMTP-Remote-Recipient-Address). Such
         fields should be used for diagnostic purposes only and not by   user
         agents or mail gateways.
  
     (c) To allow transmission of diagnostic information which is specific
         to a particular message transfer agent (MTA). The names of such
         DSN fields should begin with an indication of the MTA
         implementation that produced the DSN. (e.g. Foomail-Queue-ID).
  
     MTA implementers are encouraged to provide adequate information, via
     extension fields if necessary, to allow an MTA maintainer to understand
     the nature of correctable delivery failures and how to fix them. For
     example, if message delivery attempts are logged, the DSN might include
     information that allows the MTA maintainer to easily find the log entry
     for a failed delivery attempt.
  
     If an MTA developer does not wish to register the meanings of such
     extension fields, "X-" fields may be used for this purpose. To avoid name
     collisions, the name of the MTA implementation should follow the "X-",
     (e.g. "X-Foomail-Log-ID").
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  3. Conformance and Usage Requirements
  
     An MTA or gateway conforms to this specification if it generates DSNs
     according to the protocol defined in this memo. For MTAs and gateways
     that do not support requests for positive delivery notification (such as
     in [DRPT]), it is sufficient that delivery failure reports use this
     protocol.
  
     A minimal implementation of this specification need generate only the
     Reporting-MTA per-message field, and the Final-Recipient, Action, and
     Status fields for each attempt to deliver a message to a recipient
     described by the DSN. Generation of the other fields, when appropriate,
     is strongly recommended.
  
     MTAs and gateways MUST NOT generate the Original-Recipient field of a DSN
     unless the mail transfer protocol provides the address originally
     specified by the sender at the time of submission. (Ordinary SMTP does
     not make that guarantee, but the SMTP extension defined in [DRPT] permits
     such information to be carried in the envelope if it is available.)
  
     Each sender-specified recipient address SHOULD result in at most one
     "delivered" or "failed" DSN for that recipient. If a positive DSN is
     requested (e.g. one using NOTIFY=SUCCESS in SMTP) for a recipient that is
     forwarded to multiple recipients of an "alias" (as defined in [DRPT],
     section 7.2.7), the forwarding MTA SHOULD normally issue a "expanded" DSN
     for the originally-specified recipient and not propagate the request for
     a DSN to the forwarding addresses. Alternatively, the forwarding MTA MAY
     relay the request for a DSN to exactly one of the forwarding addresses
     and not propagate the request to the others.
  
     By contrast, successful submission of a message to a mailing list
     exploder is considered final delivery of the message. Upon delivery of a
     message to a recipient address corresponding to a mailing list exploder,
     the Reporting MTA SHOULD issue an appropriate DSN exactly as if the
     recipient address were that of an ordinary mailbox.
  
         NOTE: This is actually intended to make DSNs usable by mailing lists
         themselves. Any message sent to a mailing list subscriber should
         have its envelope return address pointing to the list maintainer
         [see RFC 1123, section 5.3.7(E)]. Since DSNs are sent to the
         envelope return address, all DSNs resulting from delivery to the
         recipients of a mailing list will be sent to the list maintainer.
         The list maintainer may elect to mechanically process DSNs upon
         receipt, and thus automatically delete invalid addresses from the
         list. (See section 7 of this memo.)
  
     This specification places no restrictions on the processing of DSNs
     received by user agents or distribution lists.
  
  
  
  
  
  
  
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  4. Security Considerations
  
     The following security considerations apply when using DSNs:
  
  4.1 Forgery
  
     DSNs may be forged as easily as ordinary Internet electronic mail. User
     agents and automatic mail handling facilities (such as mail distribution
     list exploders) that wish to make automatic use of DSNs should take
     appropriate precautions to minimize the potential damage from denial-of-
     service attacks.
  
     Security threats related to forged DSNs include the sending of:
  
     (a) A falsified delivery notification when the message is not delivered
         to the indicated recipient,
  
     (b) A falsified non-delivery notification when the message was in fact
         delivered to the indicated recipient,
  
     (c) A falsified Final-Recipient address,
  
     (d) A falsified Remote-MTA identification,
  
     (e) A falsified relay notification when the message is "dead ended".
  
     (f) Unsolicited DSNs
  
  4.2 Confidentiality
  
     Another dimension of security is confidentiality. There may be cases in
     which a message recipient is autoforwarding messages but does not wish to
     divulge the address to which the messages are autoforwarded. The desire
     for such confidentiality will probably be heightened as "wireless
     mailboxes", such as pagers, become more widely used as autoforward
     addresses.
  
     MTA authors are encouraged to provide a mechanism which enables the end
     user to preserve the confidentiality of a forwarding address. Depending
     on the degree of confidentiality required, and the nature of the
     environment to which a message were being forwarded, this might be
     accomplished by one or more of:
  
     (a) issuing a "relayed" DSN (if a positive DSN was requested) when a
         message is forwarded to a confidential forwarding address, and
         disabling requests for positive DSNs for the forwarded message,
  
     (b) declaring the message to be delivered, issuing a "delivered" DSN, re-
         sending the message to the confidential forwarding address, and
         arranging for no DSNs to be issued for the re-sent message,
  
     (c) omitting "Remote-*" or extension fields of a DSN whenever they would
         otherwise contain confidential information (such as a confidential
         forwarding address),
  
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     (d) for messages forwarded to a confidential address, setting the
         envelope return address (e.g. SMTP MAIL FROM address) to the NULL
         reverse-path ("<>") (so that no DSNs would be sent from a downstream
         MTA to the original sender),
  
     (e) for messages forwarded to a confidential address, disabling delivery
         notifications for the forwarded message (e.g. if the "next-hop" MTA
         uses ESMTP and supports the DSN extension, by using the NOTIFY=NEVER
         parameter to the RCPT command), or
  
     (f) when forwarding mail to a confidential address, having the forwarding
         MTA rewrite the envelope return address for the forwarded message
         and attempt delivery of that message as if the forwarding MTA were
         the originator. On its receipt of final delivery status, the
         forwarding MTA would issue a DSN to the original sender.
  
     In general, any optional DSN field may be omitted if the Reporting MTA
     site determines that inclusion of the field would impose too great a
     compromise of site confidentiality. The need for such confidentiality
     must be balanced against the utility of the omitted information in
     trouble reports and DSNs gatewayed to foreign environments.
  
     Implementers are cautioned that many existing MTAs will send non-delivery
     notifications to a return address in the message header (rather than to
     the one in the envelope), in violation of SMTP and other protocols. If a
     message is forwarded through such an MTA, no reasonable action on the
     part of the forwarding MTA will prevent the downstream MTA from
     compromising the forwarding address. Likewise, if the recipient's MTA
     automatically responds to messages based on a request in the message
     header (such as the nonstandard, but widely used, Return-Receipt-To
     extension header), it will also compromise the forwarding address.
  
  4.3 Non-Repudiation
  
     Within the framework of today's internet mail, the DSNs defined in this
     memo provide valuable information to the mail user; however, even a
     "failed" DSN can not be relied upon as a guarantee that a message was not
     received by the recipient. Even if DSNs are not actively forged,
     conditions exist under which a message can be delivered despite the fact
     that a failure DSN was issued.
  
     For example, a race condition in the SMTP protocol allows for the
     duplication of messages if the connection is dropped following a
     completed DATA command, but before a response is seen by the SMTP client.
     This will cause the SMTP client to retransmit the message, even though
     the SMTP server has already accepted it.[SMTPDUP] If one of those
     delivery attempts succeeds and the other one fails, a "failed" DSN could
     be issued even though the message actually reached the recipient.
  
  
  
  
  
  
  
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  5. References
  
     [DRPT] K. Moore, "SMTP Service Extension for Delivery Status
     Notifications", work-in-progress, University of Tennessee, June 2001.
  
     [DSN] K. Moore & G. Vaudreuil, "An Extensible Message Format for Delivery
     Status Notifications", RFC 1894, University of Tennessee, Octel Network
     Services, January 1996.
  
     [HOSTREQ] R. Braden (ed.), "Requirements for Internet Hosts - Application
     and Support", STD 3, RFC 1123, USC/Information Sciences Institute,
     October 1989.
  
     [MIME1] N. Freed & N. Borenstein, "Multipurpose Internet Mail Extensions
     (MIME) Part One: Format of Internet Message Bodies", RFC 2045, Bellcore,
     Innosoft, November 1996.
  
     [MIME3] K. Moore, "MIME (Multipurpose Internet Mail Extensions) Part
     Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
     University of Tennessee, November 1996.
  
     [REPORT] G. Vaudreuil, "The Multipart/Report Content Type for the
     Reporting of Mail System Administrative Messages", Work-in-Progress, June
     2001.
  
     [RFC822] D. Crocker, "Standard for the format of ARPA Internet Text
     Messages", STD 11, RFC 822, UDEL, August 1982.
  
     [SMTP] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC 821,
     USC/Information Sciences Institute, August 1982.
  
     [SMTPDUP] C. Partridge, "Duplicate Messages and SMTP", RFC 1047, BBN,
     February 1988.
  
     [STATUS] G. Vaudreuil, "Enhanced Mail System Status Codes", Work-in-
     Progress, June 2001.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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     6. Copyright Notice
  
     "Copyright (C) The Internet Society (2002). All Rights Reserved.
  
     This document and translations of it may be copied and furnished to
     others, and derivative works that comment on or otherwise explain it or
     assist in its implementation may be prepared, copied, published and
     distributed, in whole or in part, without restriction of any kind,
     provided that the above copyright notice and this paragraph are included
     on all such copies and derivative works. However, this document itself
     may not be modified in any way, such as by removing the copyright notice
     or references to the Internet Society or other Internet organizations,
     except as needed for the purpose of developing Internet standards in
     which case the procedures for copyrights defined in the Internet
     Standards process MUST be followed, or as required to translate it into
     languages other than English.
  
     The limited permissions granted above are perpetual and will not be
     revoked by the Internet Society or its successors or assigns.
  
     This document and the information contained herein is provided on an "AS
     IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
     FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
     LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
     INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
     FITNESS FOR A PARTICULAR PURPOSE."
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  7. Acknowledgments
  
     The authors wish to thank the following people for their reviews of early
     drafts of RFC 1894 and their suggestions for improvement:  Eric Allman,
     Harald Alvestrand, Allan Cargille, Jim Conklin, Peter Cowen, Dave
     Crocker, Roger Fajman, Ned Freed, Marko Kaittola, Steve Kille, John
     Klensin, John Gardiner Myers, Mark Nahabedian, Julian Onions, Jacob
     Palme, Jean Charles Roy, and Gregory Sheehan.
  
  
  
  8. Author's Address
  
     Keith Moore
     University of Tennessee
     1122 Volunteer Blvd, Suite 203
     Knoxville TN 37996-3450
     USA
     Email: moore@cs.utk.edu
  
     voice: +1-865-974-3126
     fax:   +1-865-974-8296
  
  
     Gregory M. Vaudreuil
     Lucent Technologies
     17080 Dallas Parkway
     Dallas, TX 75248-1905
     USA
     Email: GregV@ieee.org
  
     Voice: +1-972-733-2722
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Appendix A - collected grammar
  
     NOTE: The following lexical tokens are defined in RFC 822: atom, CHAR,
     comment, CR, CRLF, DIGIT, LF, linear-white-space, SPACE, text. The date-
     time lexical token is defined in [HOSTREQ].
  
          action-field = "Action" ":" action-value
  
          action-value =  "failed" / "delayed" / "delivered"
                / "relayed" / "expanded"
  
          address-type = atom
  
          arrival-date-field = "Arrival-Date" ":" date-time
  
          delivery-status-content =  per-message-fields
                1*( CRLF per-recipient-fields )
  
          diagnostic-code-field =  "Diagnostic-Code" ":"
                diagnostic-type ";" *text
  
          diagnostic-type = atom
  
          dsn-gateway-field = "DSN-Gateway" ":" mta-name-type ";" mta-name
  
          envelope-id = *text
  
          extension-field = extension-field-name ":" *text
  
          extension-field-name = atom
  
          final-recipient-field =
                "Final-Recipient" ":" address-type ";" generic-address
  
          final-log-id-field = "Final-Log-ID" ":" *text
  
          generic-address = *text
  
          last-attempt date
  
          mta-name = *text
  
          mta-name-type = atom
  
          original-envelope id
  
          original-recipient-field =
                "Original-Recipient" ":" address-type ";" generic-address
  
          per-message-fields =
                [ original-envelope-id-field CRLF ]
                reporting-mta-field CRLF
                [ dsn-gateway-field CRLF ]
                [ received-from-mta-field CRLF ]
  
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                [ arrival-date-field CRLF ]
                *( extension-field CRLF )
  
  
  
          per-recipient-fields =
               [ original-recipient-field CRLF ]
               final-recipient-field CRLF
               action-field CRLF
               status-field CRLF
               [ remote-mta-field CRLF ]
               [ diagnostic-code-field CRLF ]
               [ last-attempt-date-field CRLF ]
               [ final-log-id CRLF ]
               [ will-retry-until-field CRLF ]
                *( extension-field CRLF )
  
          received-from-mta-field =
               "Received-From-MTA" ":" mta-name-type ";" mta-name
  
          remote-mta-field =
               "Remote-MTA" ":" mta-name-type ";" mta-name
  
          reporting-mta-field =
                "Reporting-MTA" ":" mta-name-type ";" mta-name
  
          status-code = DIGIT "." 1*3DIGIT "." 1*3DIGIT
  
            ; White-space characters and comments are NOT allowed within a
            ; status-code, though a comment enclosed in parentheses MAY follow
            ; the last numeric sub-field of the status-code. Each numeric
            ; sub-field within the status-code MUST be expressed without
            ; leading zero digits.
  
          status-field = "Status" ":" status-code
  
          will-retry-until-field = "Will-Retry-Until" ":" date-time
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Appendix B - Guidelines for gatewaying DSNs
  
         NOTE: This section provides non-binding recommendations for the
         construction of mail gateways that wish to provide semi-transparent
         delivery reports between the Internet and another electronic mail
         system. Specific DSN gateway requirements for a particular pair of
         mail systems may be defined by other documents.
  
  Gatewaying from other mail systems to DSNs
  
     A mail gateway may issue a DSN to convey the contents of a "foreign"
     delivery or non-delivery notification over Internet mail. When there are
     appropriate mappings from the foreign notification elements to DSN
     fields, the information may be transmitted in those DSN fields.
     Additional information (such as might be useful in a trouble ticket or
     needed to tunnel the foreign notification through the Internet) may be
     defined in extension DSN fields. (Such fields should be given names that
     identify the foreign mail protocol, e.g. X400-* for X.400 NDN or DN
     protocol elements)
  
     The gateway must attempt to supply reasonable values for the Reporting-
     MTA, Final-Recipient, Action, and Status fields. These will normally be
     obtained by translating the values from the remote delivery or non-
     delivery notification into their Internet-style equivalents. However,
     some loss of information is to be expected. For example, the set of
     status-codes defined for DSNs may not be adequate to fully convey the
     delivery diagnostic code from the foreign system. The gateway should
     assign the most precise code which describes the failure condition,
     falling back on "generic" codes such as 2.0.0 (success), 4.0.0 (temporary
     failure), and 5.0.0 (permanent failure) when necessary. The actual
     foreign diagnostic code should be retained in the Diagnostic-Code field
     (with an appropriate diagnostic-type value) for use in trouble tickets or
     tunneling.
  
     The sender-specified recipient address, and the original envelope-id, if
     present in the foreign transport envelope, should be preserved in the
     Original-Recipient and Original-Envelope-ID fields.
  
     The gateway should also attempt to preserve the "final" recipient
     addresses and MTA names from the foreign system. Whenever possible,
     foreign protocol elements should be encoded as meaningful printable ASCII
     strings.
  
     For DSNs produced from foreign delivery or nondelivery notifications, the
     name of the gateway MUST appear in the DSN-Gateway field of the DSN.
  
  Gatewaying from DSNs to other mail systems
  
     It may be possible to gateway DSNs from the Internet into a foreign mail
     system. The primary purpose of such gatewaying is to convey delivery
     status information in a form that is usable by the destination system. A
     secondary purpose is to allow "tunneling" of DSNs through foreign mail
     systems, in case the DSN may be gatewayed back into the Internet.
  
  
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     In general, the recipient of the DSN (i.e., the sender of the original
     message) will want to know, for each recipient: the closest available
     approximation to the original recipient address, the delivery status
     (success, failure, or temporary failure), and for failed deliveries, a
     diagnostic code that describes the reason for the failure.
  
     If possible, the gateway should attempt to preserve the Original-
     Recipient address and Original-Envelope-ID (if present), in the resulting
     foreign delivery status report.
  
     When reporting delivery failures, if the diagnostic-type sub-field of the
     Diagnostic-Code field indicates that the original diagnostic code is
     understood by the destination environment, the information from the
     Diagnostic-Code field should be used. Failing that, the information in
     the Status field should be mapped into the closest available diagnostic
     code used in the destination environment.
  
     If it is possible to tunnel a DSN through the destination environment,
     the gateway specification may define a means of preserving the DSN
     information in the delivery status reports used by that environment.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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   Appendix C - Guidelines for use of DSNs by mailing list exploders
  
     This section pertains only to the use of DSNs by "mailing lists" as
     defined in [4], section 7.2.7.
  
     DSNs are designed to be used by mailing list exploders to allow them to
     detect and automatically delete recipients for whom mail delivery fails
     repeatedly.
  
     When forwarding a message to list subscribers, the mailing list exploder
     should always set the envelope return address (e.g. SMTP MAIL FROM
     address) to point to a special address which is set up to received non-
     delivery reports.  A "smart" mailing list exploder can therefore
     intercept such non-delivery reports, and if they are in the DSN format,
     automatically examine them to determine for which recipients a message
     delivery failed or was delayed.
  
     The Original-Recipient field should be used if available, since it should
     exactly match the subscriber address known to the list.  If the Original-
     Recipient field is not available, the recipient field may resemble the
     list subscriber address.  Often, however, the list subscriber will have
     forwarded his mail to a different address, or the address may be subject
     to some re-writing, so heuristics may be required to successfully match
     an address from the recipient field. Care is needed in this case to
     minimize the possibility of false matches.
  
     The reason for delivery failure can be obtained from the Status and
     Action fields, and from the Diagnostic-Code field (if the status-type is
     recognized).  Reports for recipients with action values other than
     "failed" can generally be ignored; in particular, subscribers should not
     be removed from a list due to "delayed" reports.
  
     In general, almost any failure status code (even a "permanent" one) can
     result from a temporary condition.  It is therefore recommended that a
     list exploder not delete a subscriber based on any single failure DSN
     (regardless of the status code), but only on the persistence of delivery
     failure over a period of time.
  
     However, some kinds of failures are less likely than others to have been
     caused by temporary conditions, and some kinds of failures are more
     likely to be noticed and corrected quickly than others.  Once more
     precise status codes are defined, it may be useful to differentiate
     between the status codes when deciding whether to delete a subscriber.
     For example, on a list with a high message volume, it might be desirable
     to temporarily suspend delivery to a recipient address which causes
     repeated "temporary" failures, rather than simply deleting the recipient.
     The duration of the suspension might depend on the type of error.  On the
     other hand, a "user unknown" error that persisted for several days could
     be considered a reliable indication that address were no longer valid.
  
  
  
  
  
  
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  Appendix D - IANA registration forms for DSN types
  
     The forms below are for use when registering a new address-type,
     diagnostic-type, or MTA-name-type with the Internet Assigned Numbers
     Authority (IANA).  Each piece of information requested by a registration
     form may be satisfied either by providing the information on the form
     itself, or by including a reference to a published, publicly available
     specification which includes the necessary information.  IANA MAY reject
     DSN type registrations because of incomplete registration forms,
     imprecise specifications, or inappropriate type names.
  
  
     To register a DSN type, complete the applicable form below and send
     it via Internet electronic mail to <IANA@IANA.ORG>.
  
  IANA registration form for address-type
  
     A registration for a DSN address-type MUST include the following
     information:
  
  
  (a) The proposed address-type name.
  
  (b) The syntax for mailbox addresses of this type, specified using BNF,
      regular expressions, ASN.1, or other non-ambiguous language.
  
  (c) If addresses of this type are not composed entirely of graphic
      characters from the US-ASCII repertoire, a specification for how
      they are to be encoded as graphic US-ASCII characters in a DSN
      Original-Recipient or Final-Recipient DSN field.
  
  (d) [optional] A specification for how addresses of this type are to be
      translated to and from Internet electronic mail addresses.
  
  IANA registration form for diagnostic-type
  
     A registration for a DSN address-type MUST include the following
     information:
  
  (a) The proposed diagnostic-type name.
  
  (b) A description of the syntax to be used for expressing diagnostic
      codes of this type as graphic characters from the US-ASCII
      repertoire.
  
  (c) A list of valid diagnostic codes of this type and the meaning of
      each code.
  
  (d) [optional] A specification for mapping from diagnostic codes of this
      type to DSN status codes (as defined in [5]).
  
  IANA registration form for MTA-name-type
  
  
  
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     A registration for a DSN MTA-name-type must include the following
     information:
  
  
  (a) The proposed MTA-name-type name.
  
  (b) A description of the syntax of MTA names of this type, using BNF,
      regular expressions, ASN.1, or other non-ambiguous language.
  
  (c) If MTA names of this type do not consist entirely of graphic
      characters from the US-ASCII repertoire, a specification for how an
      MTA name of this type should be expressed as a sequence of graphic
      US-ASCII characters.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Appendix E - Examples
  
     These examples are provided as illustration only, and are not considered
     part of the DSN protocol specification.  If an example conflicts with the
     protocol definition above, the example is wrong.
  
     Likewise, the use of *-type sub-field names or extension fields in these
     examples is not to be construed as a definition for those type names or
     extension fields.
  
     These examples were manually translated from bounced messages using
     whatever information was available.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Simple DSN
  
     This is a simple DSN issued after repeated attempts to deliver a message
     failed.  In this case, the DSN is issued by the same MTA from which the
     message was originated.
  
     Date: Thu, 7 Jul 1994 17:16:05 -0400
     From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
     Message-Id: <199407072116.RAA14128@CS.UTK.EDU>
     Subject: Returned mail: Cannot send message for 5 days
     To: <owner-info-mime@cs.utk.edu>
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
            boundary="RAA14128.773615765/CS.UTK.EDU"
  
     --RAA14128.773615765/CS.UTK.EDU
  
     The original message was received at Sat, 2 Jul 1994 17:10:28 -0400 from
     root@localhost
  
         ----- The following addresses had delivery problems -----
     <louisl@larry.slip.umd.edu>  (unrecoverable error)
  
         ----- Transcript of session follows -----
     <louisl@larry.slip.umd.edu>... Deferred: Connection timed out with
     larry.slip.umd.edu. Message could not be delivered for 5 days Message
     will be deleted from queue
  
     --RAA14128.773615765/CS.UTK.EDU
     content-type: message/delivery-status
  
     Reporting-MTA: dns; cs.utk.edu
  
     Original-Recipient: rfc822;louisl@larry.slip.umd.edu
     Final-Recipient: rfc822;louisl@larry.slip.umd.edu
     Action: failed
     Status: 4.0.0
     Diagnostic-Code: smtp; 426 connection timed out
     Last-Attempt-Date: Thu, 7 Jul 1994 17:15:49 -0400
  
     --RAA14128.773615765/CS.UTK.EDU
     content-type: message/rfc822
  
     [original message goes here]
  
     --RAA14128.773615765/CS.UTK.EDU--
  
  
  
  
  
  
  
  
  
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  Multi-Recipient DSN
  
     This is another DSN issued by the sender's MTA, which contains details of
     multiple delivery attempts.  Some of these were detected locally, and
     others by a remote MTA.
  
     Date: Fri, 8 Jul 1994 09:21:47 -0400
     From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
     Subject: Returned mail: User unknown
     To: <owner-ups-mib@CS.UTK.EDU>
     MIME-Version: 1.0
     Content-Type: multipart/report; report-type=delivery-status;
            boundary="JAA13167.773673707/CS.UTK.EDU"
  
     --JAA13167.773673707/CS.UTK.EDU
     content-type: text/plain; charset=us-ascii
  
         ----- The following addresses had delivery problems -----
     <arathib@vnet.ibm.com>  (unrecoverable error) <wsnell@sdcc13.ucsd.edu>
     (unrecoverable error)
  
      --JAA13167.773673707/CS.UTK.EDU
     content-type: message/delivery-status
  
     Reporting-MTA: dns; cs.utk.edu
  
     Original-Recipient: rfc822;arathib@vnet.ibm.com
     Final-Recipient: rfc822;arathib@vnet.ibm.com
     Action: failed
     Status: 5.0.0 (permanent failure)
     Diagnostic-Code: smtp;  550 'arathib@vnet.IBM.COM' is not a registered
      gateway user
     Remote-MTA: dns; vnet.ibm.com
  
     Original-Recipient: rfc822;johnh@hpnjld.njd.hp.com
     Final-Recipient: rfc822;johnh@hpnjld.njd.hp.com
     Action: delayed
     Status: 4.0.0 (hpnjld.njd.jp.com: host name lookup failure)
  
     Original-Recipient: rfc822;wsnell@sdcc13.ucsd.edu
     Final-Recipient: rfc822;wsnell@sdcc13.ucsd.edu
     Action: failed
     Status: 5.0.0
     Diagnostic-Code: smtp; 550 user unknown
     Remote-MTA: dns; sdcc13.ucsd.edu
  
     --JAA13167.773673707/CS.UTK.EDU
     content-type: message/rfc822
  
      [original message goes here]
  
     --JAA13167.773673707/CS.UTK.EDU--
  
  
  
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  DSN from gateway to foreign system
  
     A delivery report generated by Message Router (MAILBUS) and gatewayed by
     PMDF_MR to a DSN.  In this case the gateway did not have sufficient
     information to supply an original-recipient address.
  
     Disclose-recipients: prohibited
     Date: Fri, 08 Jul 1994 09:21:25 -0400 (EDT)
     From: Message Router Submission Agent <AMMGR@corp.timeplex.com>
     Subject: Status of: Re: Battery current sense
     To: owner-ups-mib@CS.UTK.EDU
     Message-id: <01HEGJ0WNBY28Y95LN@mr.timeplex.com>
     MIME-version: 1.0 content-type: multipart/report;
       report-type=delivery-status; boundary="84229080704991.122306.SYS30"
  
     --84229080704991.122306.SYS30
     content-type: text/plain
  
     Invalid address - nair_s %DIR-E-NODIRMTCH, No matching Directory Entry
     found
  
     --84229080704991.122306.SYS30
     content-type: message/delivery-status
  
     Reporting-MTA: mailbus; SYS30
  
     Final-Recipient: unknown; nair_s
     Status: 5.0.0 (unknown permanent failure)
     Action: failed
  
     --84229080704991.122306.SYS30--
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Delayed DSN
  
     A delay report from a multiprotocol MTA.  Note that there is no returned
     content, so no third body part appears in the DSN.
  
     MIME-Version: 1.0
     From: <postmaster@nsfnet-relay.ac.uk>
     Message-Id: <199407092338.TAA23293@CS.UTK.EDU>
     Received: from nsfnet-relay.ac.uk by sun2.nsfnet-relay.ac.uk
         id: <g.12954-0@sun2.nsfnet-relay.ac.uk>;
     To: owner-info-mime@cs.utk.edu
     Date: Sun, 10 Jul 1994 00:36:51 +0100
     Subject: WARNING: message delayed at "nsfnet-relay.ac.uk"
     content-type: multipart/report; report-type=delivery-status;
            boundary=foobar
  
     --foobar
     content-type: text/plain
  
     The following message:
  
     UA-ID:  Reliable PC (... Q-ID:   sun2.nsf:77/msg.11820-0 has not been
     delivered to the intended recipient: thomas@de-montfort.ac.uk despite
     repeated delivery attempts over the past 24 hours.
  
     The usual cause of this problem is that the remote system is temporarily
     unavailable.
  
     Delivery will continue to be attempted up to a total elapsed time of 168
     hours, ie 7 days.
  
     You will be informed if delivery proves to be impossible within this
     time.
  
     Please quote the Q-ID in any queries regarding this mail.
  
     --foobar
     content-type: message/delivery-status
  
     Reporting-MTA: dns; sun2.nsfnet-relay.ac.uk
  
     Final-Recipient: rfc822;thomas@de-montfort.ac.uk
     Status: 4.0.0 (unknown temporary failure)
     Action: delayed
  
     --foobar--
  
  
  
  
  
  
  
  
  
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  Appendix F - Changes from RFC1894
  
     Changed Authors contact information
  
     Updated required standards boilerplate
  
     Edited the text to make it spell-checker and grammar checker compliant
  
     Updated references to point to later, more mature documents, changed
     reference enumeration scheme.
  
     Fixed paragraph numbering on page 20
  
     Fixed Delayed DSN example
  
     Added Table of Contents
  
     Moved Appendix's to the end of the document
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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