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Versions: 00 01 02 03 04 05 06 RFC 5337

Network Working Group                                          C. Newman
Internet-Draft                                          Sun Microsystems
Updates: 3461,3464,3798                                 A. Melnikov, Ed.
(if approved)                                                  Isode Ltd
Intended status: Experimental                              June 12, 2007
Expires: December 14, 2007


          International Delivery and Disposition Notifications
                     draft-ietf-eai-dsn-01.txt

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   This Internet-Draft will expire on December 14, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Delivery status notifications (DSNs) are critical to the correct
   operation of an email system.  However, the existing draft standard
   is presently limited to US-ASCII text in the machine readable
   portions of the protocol.  This specification adds a new address type
   for international email addresses so an original recipient address
   with non-US-ASCII characters can be correctly preserved even after



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   downgrading.  This also provides updated content return media types
   for delivery status notifications and message disposition
   notifications to support use of the new address type.

   This document experimentally extends RFC 3461, RFC 3464 and RFC 3798.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in this Document  . . . . . . . . . . . . . .  3
   3.  UTF-8 Address Type . . . . . . . . . . . . . . . . . . . . . .  3
   4.  UTF-8 Delivery Status Notifications  . . . . . . . . . . . . .  5
   5.  UTF-8 Message Disposition Notifications  . . . . . . . . . . .  6
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
     6.1.  UTF-8 Mail Address Type Registration . . . . . . . . . . .  7
     6.2.  Update to 'smtp' Diagnostic Type Registration  . . . . . .  8
     6.3.  message/utf-8-headers  . . . . . . . . . . . . . . . . . .  8
     6.4.  message/utf-8-delivery-status  . . . . . . . . . . . . . .  9
     6.5.  message/utf-8-disposition-notification . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 14
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 14
   Appendix C.  Changes from -00  . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 16






















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1.  Introduction

   When an email message is transmitted using the UTF8SMTP
   [I-D.ietf-eai-smtpext] extension and Internationalized Email Headers
   [I-D.ietf-eai-utf8headers], it is sometimes necessary to return that
   message or generate a Message Disposition Notification [RFC3798]
   (MDN).  As a message sent to multiple recipients can generate a
   status and disposition notification for each recipient, it is helpful
   if a client can correlate these returns based on the recipient
   address it provided, thus preservation of the original recipient is
   important.  This specification describes how to preserve the original
   recipient and updates the MDN and DSN formats to support the new
   address types.


2.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this document are to be interpreted as defined in "Key words for
   use in RFCs to Indicate Requirement Levels" [RFC2119].

   The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC4234]
   notation including the core rules defined in Appendix B of RFC 4234
   and the rules in section 4 of RFC 3629.


3.  UTF-8 Address Type

   An Extensible Message Format for Delivery Status Notifications
   [RFC3464] defines the concept of an address type.  The address format
   introduced in Internationalized Email Headers
   [I-D.ietf-eai-utf8headers] is a new address type.  The syntax for the
   new address type in the context of status notifications follows:

   An SMTP [RFC2821] server which advertises both the UTF8SMTP extension
   [I-D.ietf-eai-smtpext] and the DSN extension [RFC3461] MUST accept a
   utf-8 address type in the ORCPT parameter including 8-bit UTF-8
   characters.  This address type also includes a 7-bit encoding
   suitable for use in a message/delivery-status body part or an ORCPT
   parameter sent to an SMTP server which does not advertise UTF8SMTP.

   This address type has 3 forms: utf-8-addr-xtext, utf-8-addr-unitext
   and utf-8-address.  The first 2 forms are 7-bit safe.

   The utf-8-address form is only suitable for use in newly defined
   protocols capable of native representation of 8-bit characters.  I.e.
   the utf-8-address form MUST NOT be used in the ORCPT parameter when
   the SMTP server doesn't advertise support for UTF8SMTP or the SMTP



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   server supports UTF8SMTP, but the address contains US-ASCII
   characters not permitted in the ORCPT parameter (e.g. the ORCPT
   parameter forbids SP and =); or in a 7-bit transport environment
   including a message/delivery-status Original-Recipient or Final-
   Recipient field.  The utf-8-addr-xtext form (see below) MUST be used
   instead in the former case, the utf-8-addr-unitext form MUST be used
   in the latter case.  The utf-8-address form MAY be used in the ORCPT
   parameter when the SMTP server also advertises support for UTF8SMTP
   and the address doesn't contains any US-ASCII characters not
   permitted in the ORCPT parameter.  It SHOULD be used in a message/
   utf-8-delivery-status Original-Recipient or Final-Recipient DSN
   field; or an Original-Recipient header field [RFC3798] if the message
   is a UTF-8 header message.

   In addition, the utf-8-addr-unitext form can be used anywhere where
   the utf-8-address form is allowed.

   When using in the ORCPT parameter, the utf-8 address type requires
   that US-ASCII CTLs, SP, %, + and = be encoded using xtext encoding as
   described in [RFC3461].  This is described by the utf-8-addr-xtext
   form in the ABNF below.  Plane 1 Unicode characters MAY be included
   in a utf-8 address type using a "%u####" syntax (QMIDCHAR, where # is
   a hexadecimal digit) and other Unicode characters MAY be encoded
   using "%U########" syntax (QHIGHCHAR).  When sending data to a
   UTF8SMTP capable server, native UTF-8 characters SHOULD be used
   instead of the QMIDCHAR and QHIGHCHAR encodings described below.
   When sending data to an SMTP server which does not advertise
   UTF8SMTP, then the QMIDCHAR and QHIGHCHAR encodings MUST be used
   instead of UTF-8.

   When the ORCPT parameter is placed in a message/utf-8-delivery-status
   Original-Recipient field, the utf-8-addr-xtext form of the utf-8
   address type SHOULD be converted to the 'utf-8-address' form (see the
   ABNF below) by removing all xtext encoding first (which will result
   in the 'utf-8-addr-unitext' form), followed by removal of the
   'unitext' encoding.  However, if an address is labeled with the utf-8
   address type but does not conform to utf-8 syntax, then it MUST be
   copied into the message/utf-8-delivery-status field without
   alteration.

   The ability to encode characters with the QMIDCHAR or QHIGHCHAR
   encodings should be viewed as a transitional mechanism.  It is hoped
   that as systems lacking support for UTF8SMTP become less common over
   time, these encodings can eventually be phased out.







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  utf-8-type-addr     = "utf-8;" utf-8-enc-addr

  utf-8-address       = uMailbox [ *WSP "<" Mailbox ">" ]
    ; 'uMailbox' is defined in [I-D.ietf-eai-smtpext].
    ; 'Mailbox' is defined in [RFC2821].

  utf-8-enc-addr      = utf-8-addr-xtext /
                        utf-8-addr-unitext /
                        utf-8-address

  ///Add comment about which where each type is used

  utf-8-addr-xtext    = xtext
                    ; xtext is defined in [RFC3461].
                    ; When xtext encoding is removed,
                    ; the syntax MUST conform to
                    ; 'utf-8-addr-unitext'.

  utf-8-addr-unitext  = 1*(QUCHAR / EmbeddedUnicodeChar)
                      ; MUST follow 'utf-8-address' ABNF when
                      ; dequoted

  ///Exclude '\'?
  QUCHAR              = %x21-2a / %x2c-3c / %x3e-7e /
                        UTF8-2 / UTF8-3 / UTF8-4
                      ; Printable except CTLs, SP, + and =

  EmbeddedUnicodeChar =   %x5C.78 "{" HEXPOINT "}"
                      ; starts with "\x"

  HEXPOINT = "5C" / ( NZHEXDIG 2*4HEXDIG ) / ( "10" 4*HEXDIG )
             ; represents either "\" or a Unicode code point outside the
             ; US-ASCII repertoire

  NZHEXDIG            = %x31-39 / "A" / "B" / "C" / "D" / "E" / "F"
                      ; HEXDIG excluding "0"


4.  UTF-8 Delivery Status Notifications

   A traditional delivery status notification [RFC3464] comes in a
   three-part multipart/report [RFC3462] container, where the first part
   is human readable text describing the error, the second part is a
   7-bit-only message/delivery-status and the optional third part is
   used for content (message/rfc822) or header (text/rfc822-headers)
   return.  An SMTP server which advertises both UTF8SMTP and DSN SHOULD
   return an undeliverable UTF8SMTP message without downgrading it
   (assuming the return SMTP server supports UTF8SMTP).  As the present



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   DSN format does not permit this, three new media types are needed.

   The first type, message/utf-8-delivery-status has the syntax of
   message/delivery-status with two modifications.  First, the charset
   for message/utf-8-delivery-status is UTF-8 and thus any field MAY
   contain UTF-8 characters when appropriate.  (In particular, the
   Diagnostic-Code field MAY contain UTF-8 as described in UTF8SMTP
   [I-D.ietf-eai-smtpext].)  Second, systems generating a message/
   utf-8-delivery-status body part SHOULD use the utf-8-address form of
   the utf-8 address type for all addresses containing characters
   outside the US-ASCII repertoire.  These systems SHOULD up-convert the
   utf-8-addr-xtext or the utf-8-addr-unitext form of a utf-8 address
   type in the ORCPT parameter to the utf-8-address form of a utf-8
   address type in the Original-Recipient field.

   The second type, used for content return, is message/utf-8 which is
   similar to message/rfc822, except it contains a message with UTF-8
   headers.  This media type is described in [I-D.ietf-eai-utf8headers].

   The third type, used for header return, is message/utf-8-headers and
   contains only the UTF-8 headers of a message (all lines prior to the
   first blank line in a UTF8SMTP message).  Unlike message/utf-8, this
   body part provides no difficulties for present infrastructure.

   All three new types will typically use the "8bit" Content-Transfer-
   Encoding (in the event all content is 7-bit, the equivalent
   traditional types for delivery status notifications are advised for
   greater backwards compatibility).  While MIME [RFC2046] advises
   against the use of 8-bit in new message subtypes intended for the
   email infrastructure, that advice does not apply to these new types
   which are intended primarily for use by newer systems with full
   support for 8-bit MIME and UTF-8 headers.


5.  UTF-8 Message Disposition Notifications

   Message Disposition Notifications [RFC3798] have a similar design and
   structure to DSNs.  As a result, they use the same basic return
   format.  When generating a MDN for a UTF-8 header message, content or
   header return is the same as for DSNs.  The second part of the
   multipart/report uses a new media type, message/
   utf-8-disposition-notification, which has the syntax of message/
   disposition-notification with two modifications.  First, the charset
   for message/utf-8-disposition-notification is UTF-8 and thus any
   field MAY contain UTF-8 characters when appropriate.  Second, systems
   generating a message/utf-8-disposition-notification body part
   (typically a mail user agent) SHOULD use the utf-8 address type for
   all addresses containing characters outside the US-ASCII repertoire.



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   The MDN specification also defines the Original-Recipient header
   field which is added with a copy of the contents of ORCPT at delivery
   time.  When generating an Original-Recipient header field, a delivery
   agent writing a UTF-8 header message in native format SHOULD convert
   the utf-8-addr-xtext or the utf-8-addr-unitext form of a utf-8
   address type in the ORCPT parameter to the corresponding utf-8-
   address form.

   The MDN specification also defines the Disposition-Notification-To
   header which is an address header and thus follows the same 8-bit
   rules as other address headers such as "From" and "To" when used in a
   UTF-8 header message.


6.  IANA Considerations

   This specification does not create any new IANA registries.  However
   the following items are registered as a result of this document:

6.1.  UTF-8 Mail Address Type Registration

   The mail address type registry was created by RFC 3464.  The
   registration template response follows:

   (a) The proposed address-type name.

   UTF-8

   (b) The syntax for mailbox addresses of this type, specified using
   BNF, regular expressions, ASN.1, or other non-ambiguous language.

   See Section 3.

   (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.

   This address type has 3 forms (as defined in Section 3): utf-8-addr-
   xtext, utf-8-addr-unitext and utf-8-address.  The first 2 forms are
   7-bit safe.

   The utf-8-address form MUST NOT be used in the ORCPT parameter when
   the SMTP server doesn't advertise support for UTF8SMTP or the SMTP
   server supports UTF8SMTP, but the address contains US-ASCII
   characters not permitted in the ORCPT parameter (e.g. the ORCPT
   parameter forbids SP and =); or in a 7-bit transport environment
   including a message/delivery-status Original-Recipient or Final-



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   Recipient field.  The utf-8-addr-xtext form MUST be used instead in
   the former case, the utf-8-addr-unitext form MUST be used in the
   latter case.  The utf-8-address form MAY be used in the ORCPT
   parameter when the SMTP server also advertises support for UTF8SMTP
   and the address doesn't contains any US-ASCII characters not
   permitted in the ORCPT parameter; in a message/utf-8-delivery-status
   Original-Recipient or Final-Recipient DSN field; or an Original-
   Recipient header field [RFC3798] if the message is a UTF-8 header
   message.

   In addition, the utf-8-addr-unitext form can be used anywhere where
   the utf-8-address form is allowed.

6.2.  Update to 'smtp' Diagnostic Type Registration

   The mail diagnostic type registry was created by RFC 3464.  The
   registration for the 'smtp' diagnostic type should be updated to
   reference RFC XXXX in addition to RFC 3464.

   When the 'smtp' diagnostic type is used in the context of a message/
   delivery-status body part, it remains as presently defined.  When the
   'smtp' diagnostic type is used in the context of a message/
   utf-8-delivery-status body part, the codes remain the same, but the
   text portion MAY contain UTF-8 characters.

6.3.  message/utf-8-headers

   Type name:  message

   Subtype name:  utf-8-headers

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  This media type contains Internationalized
      Email Headers [I-D.ietf-eai-utf8headers] with no message body.
      Whenever possible, the 8-bit content transfer encoding SHOULD be
      used.  When this media type passes through a 7-bit-only SMTP
      infrastructure it MAY be encoded with the base64 or quoted-
      printable content transfer encoding.

   Security considerations:  See Section 7

   Interoperability considerations:  It is important this media type is
      not converted to a charset other than UTF-8.  As a result,
      implementations MUST NOT include a charset parameter with this
      media type.  Although it might be possible to downconvert this



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      media type to the text/rfc822-header media type, such conversion
      is discouraged as it loses information.

   Published specification:  RFC XXXX

   Applications that use this media type:  UTF8SMTP servers and email
      clients that support multipart/report generation or parsing.

   Additional information:

   Magic number(s):  none

   File extension(s):  In the event this is saved to a file, the
      extension ".u8hdr" is suggested.

   Macintosh file type code(s):  The 'TEXT' type code is suggested as
      files of this type are typically used for diagnostic purposes and
      suitable for analysis in a UTF-8 aware text editor.  A uniform
      type identifier (UTI) of "public.utf8-email-message-header" is
      suggested.  This type conforms to "public.utf8-plain-text" and
      "public.plain-text".

   Person & email address to contact for further information:  See the
      Author's address section of this document.

   Intended usage:  COMMON

   Restrictions on usage:  This media type contains textual data in the
      UTF-8 charset.  It typically contains octets with the 8th bit set.
      As a result a transfer encoding is required when a 7-bit transport
      is used.

   Author:  See Author's Address section of this document.

   Change controller:  IETF Standards Process

6.4.  message/utf-8-delivery-status

   Type name:  message

   Subtype name:  utf-8-delivery-status

   Required parameters:  none

   Optional parameters:  none






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   Encoding considerations:  This media type contains delivery status
      notification attributes in the UTF-8 charset.  The 8-bit content
      transfer encoding MUST be used with this content-type, unless it
      is sent over a 7-bit transport environment in which case quoted-
      printable or base64 may be necessary.

   Security considerations:  See Section 7

   Interoperability considerations:  This media type provides
      functionality similar to the message/delivery-status content type
      for email message return information.  Clients of the previous
      format will need to be upgraded to interpret the new format,
      however the new media type makes it simple to identify the
      difference.

   Published specification:  RFC XXXX

   Applications that use this media type:  SMTP servers and email
      clients that support delivery status notification generation or
      parsing.

   Additional information:

   Magic number(s):  none

   File extension(s):  The extension ".u8dsn" is suggested.

   Macintosh file type code(s):  A uniform type identifier (UTI) of
      "public.utf8-email-message-delivery-status" is suggested.  This
      type conforms to "public.utf8-plain-text".

   Person & email address to contact for further information:  See the
      Author's address section of this document.

   Intended usage:  COMMON

   Restrictions on usage:  This is expected to be the second part of a
      multipart/report.

   Author:  See Author's Address section of this document.

   Change controller:  IETF Standards Process

6.5.  message/utf-8-disposition-notification







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   Type name:  message

   Subtype name:  utf-8-disposition-notification

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  This media type contains disposition
      notification attributes in the UTF-8 charset.  The 8-bit content
      transfer encoding MUST be used with this content-type, unless it
      is sent over a 7-bit transport environment in which case quoted-
      printable or base64 may be necessary.

   Security considerations:  See Section 7

   Interoperability considerations:  This media type provides
      functionality similar to the message/disposition-notification
      content type for email message disposition information.  Clients
      of the previous format will need to be upgraded to interpret the
      new format, however the new media type makes it simple to identify
      the difference.

   Published specification:  RFC XXXX

   Applications that use this media type:  Email clients or servers that
      support message disposition notification generation or parsing.

   Additional information:

   Magic number(s):  none

   File extension(s):  The extension ".u8mdn" is suggested.

   Macintosh file type code(s):  A uniform type identifier (UTI) of
      "public.utf8-email-message-disposition-notification" is suggested.
      This type conforms to "public.utf8-plain-text".

   Person & email address to contact for further information:  See the
      Author's address section of this document.

   Intended usage:  COMMON

   Restrictions on usage:  This is expected to be the second part of a
      multipart/report.






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   Author:  See Author's Address section of this document.

   Change controller:  IETF Standards Process


7.  Security Considerations

   Automated use of report types without authentication presents several
   security issues.  Forging negative reports presents the opportunity
   for denial-of-service attacks when the reports are used for automated
   maintenance of directories or mailing lists.  Forging positive
   reports may cause the sender to incorrectly believe a message was
   delivered when it was not.

   Malicious users can generate report structures designed to trigger
   coding flaws in report parsers.  Report parsers need to use secure
   coding techniques to avoid the risk of buffer overflow or denial-of-
   service attacks against parser coding mistakes.  Code reviews of such
   parsers are also recommended.

   Malicious users of the email system regularly send messages with
   forged envelope return paths and these messages trigger delivery
   status reports that result in a large amount of unwanted traffic on
   the Internet.  Many users choose to ignore delivery status
   notifications because they are usually the result of "blowback" from
   forged messages and thus never notice when messages they sent go
   undelivered.  As a result, support for correlation of delivery status
   and message disposition notification messages with sent-messages has
   become a critical feature of mail clients and possibly mail stores if
   the email infrastructure is to remain reliable.  In the short term,
   simply correlating message-IDs may be sufficient to distinguish true
   status notifications from those resulting from forged originator
   addresses.  But in the longer term, including cryptographic signature
   material that can securely associate the status notification with the
   original message is advisable.

   As this specification permits UTF-8 in additional fields, the
   security considerations of UTF-8 [RFC3629] apply.


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2821]  Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,



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              April 2001.

   [RFC3461]  Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
              Extension for Delivery Status Notifications (DSNs)",
              RFC 3461, January 2003.

   [RFC3462]  Vaudreuil, G., "The Multipart/Report Content Type for the
              Reporting of Mail System Administrative Messages",
              RFC 3462, January 2003.

   [RFC3464]  Moore, K. and G. Vaudreuil, "An Extensible Message Format
              for Delivery Status Notifications", RFC 3464,
              January 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3798]  Hansen, T. and G. Vaudreuil, "Message Disposition
              Notification", RFC 3798, May 2004.

   [RFC4234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [I-D.ietf-eai-utf8headers]
              Yang, A., "Internationalized Email Headers",
              draft-ietf-eai-utf8headers-05 (work in progress),
              April 2007.

   [I-D.ietf-eai-smtpext]
              Yao, J. and W. Mao, "SMTP extension for internationalized
              email address", draft-ietf-eai-smtpext-05 (work in
              progress), April 2007.

   [I-D.ietf-eai-downgrade]
              Yoneya, Y. and K. Fujiwara, "Downgrading mechanism for
              Email Address Internationalization (EAI)",
              draft-ietf-eai-downgrade-03 (work in progress), Mar 2007.

8.2.  Informative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.




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   [RFC3501]  Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
              4rev1", RFC 3501, March 2003.


Appendix A.  Acknowledgements

   Many thanks for input provided by Pete Resnick, James Galvin, Ned
   Freed, John Klensin and members of the EAI WG to help solidify this
   proposal.


Appendix B.  Open Issues

   Suggestion to change the utf-8-addr format from \-encoded Unicode to
   \-encoded UTF-8 as used in URIs.

   Use a single syntax for I18N addresses in ORCPT/DSN instead of two
   (Chris)

   Potential issue: an SMTP server can't deliver an EAI DSN to the next
   hop - need to use a 7bit encoding, downgrade or discard?  Need to
   describe choices.

   Tracker issue #1485: UTF8HDR 4.6/DSN: Choice of body part for
   transport of UTF8SMTP messages

   Tracker issue #1483: SMTPEXT 2.7: Non-ASCII in response texts


Appendix C.  Changes from -00

   Added paragraph about use of 8bit Content-Transfer-Encoding for new
   message sub-types.

   Updated the list of open issues.

   Clarified that this document is targeted to become an Experimental
   RFC.

   Made the EAI downgrade document a normative reference.

   Updated ABNF for utf-8-address.









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Authors' Addresses

   Chris Newman
   Sun Microsystems
   3401 Centrelake Dr., Suite 410
   Ontario, CA  91761
   US

   Email: chris.newman@sun.com


   Alexey Melnikov (editor)
   Isode Ltd
   5 Castle Business Village
   36 Station Road
   Hampton, Middlesex  TW12 2BX
   UK

   Email: Alexey.Melnikov@isode.com
































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