Internationalized DSNs: Internationalized Delivery Status and Disposition Notifications

Internet Engineering Task Force (IETF)                    T. Hansen, Ed.
Request for Comments: 6533                             AT&T Laboratories
Obsoletes: 5337                                                C. Newman
Updates: 3461, 3464, 3798, 6522                                   Oracle
Category: Standards Track                                    A. Melnikov
ISSN: 2070-1721                                                Isode Ltd
                                                           February 2012


    Internationalized Delivery Status and Disposition Notifications

Abstract

   Delivery status notifications (DSNs) are critical to the correct
   operation of an email system.  However, the existing Draft Standards
   (RFC 3461, RFC 3464, RFC 6522) are presently limited to 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-ASCII characters can be correctly
   preserved even after 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 extends RFC 3461, RFC 3464, RFC 3798, and RFC 6522.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6533.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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  . . . . . . . . . . . . .  6
     4.1.  The message/global-delivery-status Media Type  . . . . . .  6
     4.2.  The message/global Media Type  . . . . . . . . . . . . . .  8
     4.3.  The message/global-headers Media Type  . . . . . . . . . .  8
     4.4.  Using These Media Types with multipart/report  . . . . . .  8
     4.5.  Additional Requirements on SMTP Servers  . . . . . . . . .  9
   5.  UTF-8 Message Disposition Notifications  . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  UTF-8 Mail Address Type Registration . . . . . . . . . . . 10
     6.2.  Update to 'smtp' Diagnostic Type Registration  . . . . . . 11
     6.3.  message/global-headers . . . . . . . . . . . . . . . . . . 11
     6.4.  message/global-delivery-status . . . . . . . . . . . . . . 12
     6.5.  message/global-disposition-notification  . . . . . . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  Changes since RFC 5337  . . . . . . . . . . . . . . . 18
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 18

1.  Introduction

   When an email message is transmitted using the SMTPUTF8 [RFC6531]
   extension and Internationalized Email Headers [RFC6532], it is
   sometimes necessary to return that message or generate a Message
   Disposition Notification (MDN) [RFC3798].  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 notifications 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.

   NOTE: While this specification updates the experimental versions of
   this protocol by removing certain constructs (e.g., the "<addr
   <addr>>" address syntax is no longer permitted), the name of the
   Address Type "UTF-8" and the media type names message/global,
   message/global-delivery-status, and message/global-headers have not
   been changed.

   This specification is a revision of and replacement for [RFC5337].
   Section 6 of [RFC6530] describes the change in approach between this
   specification and the previous version.

2.  Conventions Used in This Document

   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 [RFC2119].

   The formal syntax uses the Augmented Backus-Naur Form (ABNF)
   [RFC5234] notation including the core rules defined in Appendix B of
   [RFC5234] and the UTF-8 syntax rules in Section 4 of [RFC3629].

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" [RFC6532] is a new
   address type.  The syntax for the new address type in the context of
   status notifications is specified at the end of this section.

   An SMTP [RFC5321] server that advertises both the SMTPUTF8 extension
   [RFC6531] 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 that does not advertise SMTPUTF8.

   This address type has 3 forms: utf-8-addr-xtext, utf-8-addr-unitext,
   and utf-8-address.  Only the first form is 7-bit safe (only uses
   ASCII characters [ASCII]).

   The utf-8-address form is only suitable for use in newly defined
   protocols capable of native representation of 8-bit characters.  That
   is, the utf-8-address form MUST NOT be used:

   1.  in the ORCPT parameter when the SMTP server doesn't advertise
       support for SMTPUTF8 (utf-8-addr-xtext MUST be used instead); or

   2.  if the SMTP server supports SMTPUTF8, but the address contains
       ASCII characters not permitted in the ORCPT parameter (e.g., the
       ORCPT parameter forbids unencoded SP and the '=' character),
       (either utf-8-addr-unitext or utf-8-addr-xtext MUST be used
       instead); or

   3.  in a 7-bit transport environment including a message/
       delivery-status "Original-Recipient:" or "Final-Recipient:"
       field, (utf-8-addr-xtext MUST be used instead).

   The utf-8-address form MAY be used in the ORCPT parameter when the
   SMTP server also advertises support for SMTPUTF8 and the address
   doesn't contain any ASCII characters not permitted in the ORCPT
   parameter.  It SHOULD be used in a message/global-delivery-status
   "Original-Recipient:" or "Final-Recipient:" DSN field, or in an
   "Original-Recipient:" header field [RFC3798] if the message is a
   SMTPUTF8 message.

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

   When used in the ORCPT parameter, the UTF-8 address type requires
   that ASCII CTLs, SP, '\', '+', and '=' be encoded using 'unitext'
   encoding (see below).  This is described by the utf-8-addr-xtext and
   utf-8-addr-unitext forms in the ABNF below.  The 'unitext' encoding
   uses "\x{HEXPOINT}" syntax (EmbeddedUnicodeChar in the ABNF below)
   for encoding any Unicode character outside of ASCII range, as well as
   for encoding CTLs, SP, '\', '+', and '='.  HEXPOINT is 2 to 6
   hexadecimal digits.  This encoding avoids the need to use the xtext
   encoding described in [RFC3461], as any ASCII characters that need to
   be escaped using xtext encoding never appear in any unitext-encoded
   string.  When sending data to a SMTPUTF8-capable server, native UTF-8
   characters SHOULD be used instead of the EmbeddedUnicodeChar syntax
   described below.  When sending data to an SMTP server that does not
   advertise SMTPUTF8, then the EmbeddedUnicodeChar syntax MUST be used
   instead of UTF-8.

   When the ORCPT parameter is placed in a message/
   global-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 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/global-delivery-status field without
   alteration.

   The ability to encode characters with the EmbeddedUnicodeChar
   encodings should be viewed as a transitional mechanism and avoided
   when possible.  It is hoped that as systems lacking support for
   SMTPUTF8 become less common over time, these encodings can eventually
   be phased out.

   In the ABNF below, all productions not defined in this document are
   defined in Appendix B of [RFC5234], in Section 4 of [RFC3629], or in
   [RFC3464].

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

   utf-8-address       = Mailbox
     ; Mailbox as defined in [RFC6531].

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

   utf-8-addr-xtext    = 1*(QCHAR / EmbeddedUnicodeChar)
                         ; 7bit form of utf-8-addr-unitext.
                         ; Safe for use in the ORCPT [RFC3461]
                         ; parameter even when SMTPUTF8 SMTP
                         ; extension is not advertised.

   utf-8-addr-unitext  = 1*(QUCHAR / EmbeddedUnicodeChar)
                       ; MUST follow utf-8-address ABNF when
                       ; dequoted.
                       ; Safe for using in the ORCPT [RFC3461]
                       ; parameter when SMTPUTF8 SMTP extension
                       ; is also advertised.

   QCHAR              = %x21-2a / %x2c-3c / %x3e-5b / %x5d-7e
                       ; ASCII printable characters except
                       ; CTLs, SP, '\', '+', '='.

   QUCHAR              = QCHAR / UTF8-2 / UTF8-3 / UTF8-4
                       ; ASCII printable characters except
                       ; CTLs, SP, '\', '+' and '=', plus
                       ; other Unicode characters encoded in UTF-8

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

   HEXPOINT = ( ( "0"/"1" ) %x31-39 ) / "10" / "20" /
              "2B" / "3D" / "7F" /         ; all xtext-specials
              "5C" / (HEXDIG8 HEXDIG) /    ; 2-digit forms
              ( NZHEXDIG 2(HEXDIG) ) /     ; 3-digit forms
              ( NZDHEXDIG 3(HEXDIG) ) /    ; 4-digit forms excluding
              ( "D" %x30-37 2(HEXDIG) ) /  ; ... surrogate
              ( NZHEXDIG 4(HEXDIG) ) /     ; 5-digit forms
              ( "10" 4*HEXDIG )            ; 6-digit forms
              ; represents either "\" or a Unicode code point outside
              ; the ASCII repertoire

   HEXDIG8             = %x38-39 / "A" / "B" / "C" / "D" / "E" / "F"
                       ; HEXDIG excluding 0-7
   NZHEXDIG            = %x31-39 / "A" / "B" / "C" / "D" / "E" / "F"
                       ; HEXDIG excluding "0"
   NZDHEXDIG           = %x31-39 / "A" / "B" / "C" / "E" / "F"
                       ; HEXDIG excluding "0" and "D"

4.  UTF-8 Delivery Status Notifications

   A traditional delivery status notification [RFC3464] comes in a
   three-part multipart/report [RFC6522] 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.  As the present standard DSN format does not permit the
   return of undeliverable SMTPUTF8 messages, three new media types have
   been defined.  ([RFC5337] introduced experimental versions of these
   media types.)

4.1.  The message/global-delivery-status Media Type

   The first type, message/global-delivery-status, has the syntax of
   message/delivery-status with three modifications.  First, the charset
   for message/global-delivery-status is UTF-8, and thus any field MAY
   contain UTF-8 characters when appropriate (see the ABNF below).  In
   particular, the "Diagnostic-Code:" field MAY contain UTF-8 as
   described in SMTPUTF8 [RFC6531]; the "Diagnostic-Code:" field SHOULD
   be in i-default language [RFC2277].  Second, systems generating a
   message/global-delivery-status body part SHOULD use the utf-8-address
   form of the UTF-8 address type for all addresses containing
   characters outside the 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.  Third,
   an optional field called "Localized-Diagnostic:" is added.  Each
   instance includes a language tag [RFC5646] and contains text in the
   specified language.  This is equivalent to the text part of the
   "Diagnostic-Code:" field.  All instances of "Localized-Diagnostic:"
   MUST use different language tags.  The ABNF for message/
   global-delivery-status is specified below.

   In the ABNF below, all productions not defined in this document are
   defined in Appendix B of [RFC5234], in Section 4 of [RFC3629], or in
   [RFC3464].  Note that <text-fixed> is the same as <text> from
   [RFC5322], but without <obs-text>.  If or when RFC 5322 is updated to
   disallow <obs-text>, <text-fixed> should become just <text>.  Also,
   if or when RFC 5322 is updated to disallow control characters in
   <text>, <text-fixed> should become a reference to that update
   instead.

   utf-8-delivery-status-content = per-message-fields
                         1*( CRLF utf-8-per-recipient-fields )
        ; "per-message-fields" remains unchanged from the definition
        ; in RFC 3464, except for the "extension-field",
        ; which is updated below.

   utf-8-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
           *(localized-diagnostic-text-field CRLF) ]
         [ last-attempt-date-field CRLF ]
             [ final-log-id-field CRLF ]
         [ will-retry-until-field CRLF ]
         *( extension-field CRLF )
     ; All fields except for "original-recipient-field",
     ; "final-recipient-field", "diagnostic-code-field",
     ; and "extension-field" remain unchanged from
     ; the definition in RFC 3464.

   generic-address =/ utf-8-enc-addr
     ; Only allowed with the "utf-8" address-type.
     ; Updates Section 3.2.3 of RFC 3798.
     ;
     ; This indirectly updates "original-recipient-field"
     ; and "final-recipient-field".

   diagnostic-code-field =
        "Diagnostic-Code" ":" diagnostic-type ";" *text-fixed

   localized-diagnostic-text-field =
        "Localized-Diagnostic" ":" Language-Tag ";" *utf8-text
     ; "Language-Tag" is a language tag as defined in [RFC5646].

   extension-field =/ extension-field-name ":" *utf8-text
     ; Updates Section 7 of RFC3798

   text-fixed = %d1-9 /      ; Any ASCII character except for NUL,
                %d11 /       ; CR, and LF.
                %d12 /       ; See note above about <text-fixed>
                %d14-127

   utf8-text = text-fixed / UTF8-non-ascii

   UTF8-non-ascii   = UTF8-2 / UTF8-3 / UTF8-4

4.2.  The message/global Media Type

   The second type, used for returning the content, is message/global,
   which is similar to message/rfc822, except it contains a message with
   UTF-8 headers.  This media type is described in [RFC6532].

4.3.  The message/global-headers Media Type

   The third type, used for returning the headers, is message/
   global-headers and contains only the UTF-8 header fields of a message
   (all lines prior to the first blank line in a SMTPUTF8 message).
   Unlike message/global, this body part provides no difficulties for
   the present infrastructure.

4.4.  Using These Media Types with multipart/report

   Note that as far as a multipart/report [RFC6522] container is
   concerned, message/global-delivery-status, message/global, and
   message/global-headers MUST be treated as equivalent to message/
   delivery-status, message/rfc822, and text/rfc822-headers.  That is,
   implementations processing multipart/report MUST expect any
   combinations of the 6 media types mentioned above inside a multipart/
   report media type.

   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 MAY be used.  For
   example, if information in a message/global-delivery-status part can
   be represented without any loss of information as message/
   delivery-status, then the message/delivery-status body part may be
   used.)  Note that [RFC6532] relaxed a restriction from MIME [RFC2046]
   regarding the use of Content-Transfer-Encoding in new "message"
   subtypes.  This specification explicitly allows the use of Content-
   Transfer-Encoding in message/global-headers and message/
   global-delivery-status.  This is not believed to be problematic as
   these new media types are intended primarily for use by newer systems
   with full support for 8-bit MIME and UTF-8 headers.

4.5.  Additional Requirements on SMTP Servers

   If an SMTP server that advertises both SMTPUTF8 and DSN needs to
   return an undeliverable SMTPUTF8 message, then it has two choices for
   encapsulating the SMTPUTF8 message when generating the corresponding
   multipart/report:

      If the return-path SMTP server does not support SMTPUTF8, then the
      undeliverable body part and headers MUST be encoded using a 7-bit
      Content-Transfer-Encoding such as "base64" or "quoted-printable"
      [RFC2045], as detailed in Section 4.

      Otherwise, "8bit" Content-Transfer-Encoding can be used.

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 an MDN for a UTF-8 header message, the third
   part of the multipart/report contains the returned content (message/
   global) or header (message/global-headers), same as for DSNs.  The
   second part of the multipart/report uses a new media type, message/
   global-disposition-notification, which has the syntax of message/
   disposition-notification with two modifications.  First, the charset
   for message/global-disposition-notification is UTF-8, and thus any
   field MAY contain UTF-8 characters when appropriate (see the ABNF
   below).  (In particular, the failure-field, the error-field, and the
   warning-field MAY contain UTF-8.  These fields SHOULD be in i-default
   language [RFC2277].)  Second, systems generating a message/
   global-disposition-notification body part (typically a mail user
   agent) SHOULD use the UTF-8 address type for all addresses containing
   characters outside the ASCII repertoire.

   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 field, which is an address header field and thus follows the
   same 8-bit rules as other address header fields such as "From:" and
   "To:" when used in a UTF-8 header message.

     ; ABNF for "original-recipient-header", "original-recipient-field",
     ; and "final-recipient-field" from RFC 3798 is implicitly updated
     ; as they use the updated "generic-address" as defined in
     ; Section 4 of this document.

   failure-field = "Failure" ":" *utf8-text
     ; "utf8-text" is defined in Section 4 of this document.

   error-field = "Error" ":" *utf8-text
     ; "utf8-text" is defined in Section 4 of this document.

   warning-field = "Warning" ":" *utf8-text
     ; "utf8-text" is defined in Section 4 of this document.

6.  IANA Considerations

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

6.1.  UTF-8 Mail Address Type Registration

   The mail address type registry was created by [RFC3464].  The
   registration template response follows:

   (a) The 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 ASCII repertoire, a specification for how
       they are to be encoded as graphic ASCII characters in an
       "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.  Only
       the first form is 7-bit safe.

6.2.  Update to 'smtp' Diagnostic Type Registration

   The mail diagnostic type registry was created by [RFC3464] and
   updated by [RFC5337].  This specification replaces [RFC5337].  The
   registration for the 'smtp' diagnostic type has been updated to
   reference RFC 6533 in addition to [RFC3464] and to remove the
   reference to [RFC5337].

   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/
   global-delivery-status body part, the codes remain the same, but the
   text portion MAY contain UTF-8 characters.

6.3.  message/global-headers

   Type name:  message

   Subtype name:  global-headers

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  This media type contains Internationalized
      Email Headers [RFC6532] 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 that 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 down-convert this
      media type to the text/rfc822-header media type, such conversion
      is discouraged as it loses information.

   Published specification:  RFC 6533

   Applications that use this media type:  SMTPUTF8 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
      Authors' Addresses 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 the Authors' Addresses section of this document.

   Change controller:  IETF Standards Process

6.4.  message/global-delivery-status

   Type name:  message

   Subtype name:  global-delivery-status

   Required parameters:  none
   Optional parameters:  none

   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 6533

   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
      Authors' Addresses section of this document.

   Intended usage:  COMMON

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

   Author:  See the Authors' Addresses section of this document.

   Change controller:  IETF Standards Process

6.5.  message/global-disposition-notification

   Type name:  message

   Subtype name:  global-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 6533

   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
      Authors' Addresses section of this document.

   Intended usage:  COMMON

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

   Author:  See the Authors' Addresses 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

   [ASCII]    American National Standards Institute (formerly United
              States of America Standards Institute), "USA Code for
              Information Interchange", ANSI X3.4-1968, 1968.

              ANSI X3.4-1968 has been replaced by newer versions with
              slight modifications, but the 1968 version remains
              definitive for the Internet.

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

   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, January 1998.

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

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              October 2008.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

   [RFC6522]  Kucherawy, M., Ed., "The Multipart/Report Media Type for
              the Reporting of Mail System Administrative Messages", STD
              73, RFC 6522, January 2012.

   [RFC6530]  Klensin, J. and Y. Ko, "Overview and Framework for
              Internationalized Email", RFC 6530, February 2012.

   [RFC6531]  Yao, J. and W. Mao, "SMTP Extension for Internationalized
              Email", RFC 6531, February 2012.

   [RFC6532]  Yang, A., Steele, S., and N. Freed, "Internationalized
              Email Headers", RFC 6532, February 2012.

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.

   [RFC5337]  Newman, C. and A. Melnikov, "Internationalized Delivery
              Status and Disposition Notifications", RFC 5337,
              September 2008.

Appendix A.  Changes since RFC 5337

   Changes were made to move from Experimental to Standards Track.  The
   most significant was the removal of an embedded alternative ASCII
   address within a utf-8-address, and the reflections of the ABNF
   changes in [RFC6531].

   Fixed description of utf-8-addr-xtext and utf-8-addr-unitext.

   References to Downgrade and uMailbox removed/fixed.

   ABNF changes and fixed errata submitted by Alfred Hoenes.

   Minor changes to MIME type references.

   Other minor corrections.

Appendix B.  Acknowledgements

   Many thanks for input provided by Pete Resnick, James Galvin, Ned
   Freed, John Klensin, Harald Alvestrand, Frank Ellermann, SM, Alfred
   Hoenes, Kazunori Fujiwara, and members of the EAI working group to
   help solidify this proposal.

Authors' Addresses

   Tony Hansen (editor)
   AT&T Laboratories
   200 Laurel Ave.
   Middletown, NJ  07748
   US

   EMail: tony+eaidsn@maillennium.att.com


   Chris Newman
   Oracle
   800 Royal Oaks
   Monrovia, CA  91016-6347
   US

   EMail: chris.newman@oracle.com


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

   EMail: Alexey.Melnikov@isode.com