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Network Working Group                                        Keith Moore
Internet Draft                                   University of Tennessee
Expires: May 20, 20 July 1995                                     Greg Vaudreuil
                                                  Octel Network Services
                                                       November 20, 1994
                                                         20 January 1995


                      An Extensible Message Format
                   for Delivery Status Notifications

                 draft-ietf-notary-mime-delivery-03.txt

                 draft-ietf-notary-mime-delivery-04.txt


Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as ``work in progress.''

To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).


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
meant to be intended as a machine-processable alternative to replacement for the full range
various types of
electronic mail delivery status notifications currently used in use
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
Internet. 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.








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1. Introduction

This memo defines a MIME [1] 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 [2].

This memo defines only the format of the notifications.  An extension to
the Simple Message Transfer Protocol (SMTP) [3] to fully support such
notifications is the subject of a separate memo [4].



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Because many messages are sent between the MIME-capable world and other
messaging systems (such as X.400 or the so-called "LAN-based" systems),
the DSN protocol is intended to be useful in a multi-protocol messaging
environment.  To this end, the DSN protocol provides for the carriage of
"foreign" addresses and error codes, in addition to the addresses and
error codes normally used in Internet mail.   Additional attributes may
also be defined to support "tunneling" of foreign notifications through
MIME-capable systems using the DSN protocol.


2. Requirements


1.1. Purposes

The DSNs defined in this memo are expected to serve several purposes:

+ Inform human beings of the status of message delivery processing, as
  well as the reasons for any delivery problems or outright failures failures, in
  a manner which is largely language-independent;

+ Allow mail user agents to keep track of the delivery status of
  messages sent sent, by associating returned DSNs with earlier message
  transmissions;

+ Allow mailing list expanders to automatically maintain their
  subscriber lists when delivery attempts fail repeatedly fail;

+ Convey delivery and non-delivery notifications resulting from attempts
  to deliver messages to "foreign" mail systems via a gateway gateway;

+ 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;

+ Allow language-independent, yet reasonably precise, indications of the
  reason for the failure of a message to be delivered (once status codes
  of sufficient precision are defined); and

+ 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.

These purposes place the following constraints on the notification
protocol:

+








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1.2. Requirements

These purposes place the following constraints on the notification
protocol:

+ It must be readable by humans as well as being machine-parsable.

+ 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.

+ It must be able to preserve the information associated with reason for the success or failure of a
  delivery attempt in a remote messaging system, using the "language" (addresses
  (mailbox addresses and status codes) of that remote system.




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+ 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.

+ 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.

+ 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 original system, foreign addresses and error codes, so that the "foreign" attributes
  mentioned above these may
  be correctly interpreted. interpreted by gateways.

A DSN consists of contains a set of per-message fields to which 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, message to each of one or more recipients.


1.3. Terminology

A message that is either gatewayed between dissimilar messaging systems
or auto-forwarded to an alternate recipient address may have be transmitted through several message transfer agents
(MTAs) on its sender
or way to a recipient.  For a variety of reasons, recipient
addresses changed may be rewritten during transit.  For any particular
recipient, up to three 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 an a particular recipient
address will be needed.

Several DSN fields are defined in terms of interest:

"original"  The recipient address as originally specified by the sender.

"final"     The recipient address as it was when view from a particular
MTA in the message was
            presented to transmission.  The MTAs are assigned the "final" following names:




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a. Original MTA

The Original MTA is the one to handle which the message is submitted for that
            recipient (i.e.,
delivery by the one which is issuing sender of the DSN).

"remote"    If an attempt was made by message.

Note: Each time a message is re-sent to a completely different set of
recipients (say to the "final" subscribers of a mailing list), the Original MTA
for the new recipients of that message is the one to relay which the message
is initially submitted for delivery to yet another MTA, and the new list of recipients.

b. Reporting MTA

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 is issued was produced by translating the
            "final"
foreign notice into DSN format, the Reporting MTA based on will still identify
the response "foreign" MTA where the delivery attempts occurred.

c. Preceding MTA

The Preceding MTA is the MTA from which the Reporting MTA received the
message, and accepted responsibility for delivery of the "remote" (next-hop) 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 address presented "next hop" MTA refuses to accept responsibility for delivery
of the "remote" MTA, along with message to one or more of its intended recipients, the status code returned by that MTA, relaying
MTA may also be need to issue a DSN on behalf of
            interest. 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 may be useful in explaining illustrates the difference relationship between the
"original", "final", and "remote" various MTAs:


+-----+    +--------+           +-----------+    +-----+           +---------+    +---------+      +------+
|     | => |Original| => ... => |penultimate| |Preceding| => |Final| |Reporting| ===> |Remote|
| user|    |   MTA  |           |   MTA   |    |   MTA   | <No! |  MTA |
|agent|    +--------+           +-----------+    +--v--+           +---------+    +----v----+      +------+
|     |                                             |
|     | <-------------------------------------------+
+-----+      (DSN returned to sender by Final Reporting MTA)


       Figure 1. Illustration of  Original, Final, Preceding, Reporting and Remote MTAs


In the diagram, the "original" MTA is the one


Each of these MTAs may provide information which accepts is useful in a DSN:



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+ Ideally, the message
from DSN will contain the sender's user agent.  The message successfully passes through
perhaps several other MTAs until it arrives at the "final" MTA, which
for some reason needs to issue a DSN.  The DSN is returned address of each recipient as
  originally specified to the
sender.  (By definition, the MTA that issues a DSN is always the "final"
MTA.)



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If the "final" MTA is issuing the DSN based on information obtained from
some other Original MTA downstream (for example, because by the downstream MTA
refused to accept responsibility for delivery sender of a message), then the
MTA which reported that information is the "remote" MTA.  (If the
"final" MTA issues the DSN based on information obtained locally, as in the case of delivery to a local user, there is no "remote" MTA.)

Each message.
  This version of these addresses is useful under some circumstances:

+ The DSN must contain the original recipient address is needed (rather than a forwarding
  address or some modified version of the original address), address) so that the
  sender may compare the recipient address in the DSN can be compared with the
  recipient address as specified by the sender when the original message
  was sent.

+ The "final" form of
  in the sender's records (e.g. an address is needed when reporting a problem to book for an individual, the postmaster
  list of subscribers for a mailing list) and take appropriate action.

  Similarly, the site where message delivery failed, so DSN may contain an "envelope identifier" that she
  can attempt was known
  to reproduce the conditions that caused the failure.

+ When interpreting a DSN, both the sender's user agent will want and the latest
  possible (i.e. "remote") status code Original MTA at the time of
  message submission, and which if it is available.  However,
  this code may either not included in the DSN, can be available, used by
  the sender to keep track of which messages were or it might be from were not delivered.

+ If a foreign message was (a) forwarded to a different address than that
  specified by the sender, (b) gatewayed to a different mail system whose codes are not understood 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.
  In these cases agent
  (or the sender) prefers the original recipient address, so the "final" code might be more useful.

+ When gatewaying
  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 "failure" DSN into should contain the most accurate explanation for the
  delivery failure that is available.  For ease of interpretation, this
  information should be a foreign MTS, format which is independent of the gateway may use either mail
  transport system that issued the "remote" or "final" 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 codes code and recipient addresses,
  depending a mechanism for reporting
  transport-specific codes.  Depending on circumstances.  Similarly, it may the circumstances that
  produced delivery failure, the transport-specific code might be appropriate to use
  obtained from either the original Reporting MTA or the current recipient address for any
  particular recipient.  This situation is described in more detail in
  Appendix 13. Remote MTA.

Since different values for "sender address", "recipient address", 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 allows
each of several different may contain both the
original and final forms of the sender address, a recipient address, and status code to be conveyed.


3. Format of both a Delivery Status Notification

A complete DSN is transport-
independent and a MIME message with a top-level content-type of
multipart/report (defined in [2]).  For a DSN, the report-type parameter transport-specific indication of the multipart/report content is "delivery-status".

A particular DSN describes the delivery status for exactly one message.
However, an MTA MAY report on status.

Extension fields may also be added by the delivery status Reporting MTA as needed to
provide additional information for several recipients
of the same message use in a single DSN.  Due trouble ticket or to the nature of the mail
transport system (where responsibility
preserve information for delivery tunneling of a message to its
recipients foreign delivery reports through
Internet DSNs.

The Original, Reporting, and Remote MTAs may be split among several MTAs, exist in very different
environments and use dissimilar transport protocols, MTA names, address
formats, and delivery to status codes.  DSNs therefore do not assume any



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particular recipient may be delayed), multiple DSNs format for mailbox addresses, MTA names, or transport-
specific status codes.  Instead, the various DSN fields that carry such
quantities consist of a "type" subfield followed by a subfield whose
contents may be still be
issued.

The DSN any octet string, and whose format is addressed (in both indicated by the header and envelope)
"type" subfield.  This allows a DSN to the return
address from the envelope convey these quantities
regardless of the format.


2. Format of a Delivery Status Notification

A DSN is a MIME message for which with a top-level content-type of
multipart/report (defined in [2]).  When a multipart/report content is
used to transmit a DSN:

+ The report-type parameter of the DSN multipart/report content is being
generated.
  "delivery-status".

+ The From header field first component of the DSN multipart/report contains a human-readable
  explanation of the address DSN, as described in [5].

+ The second component of a
human who is responsible for maintaining the mail system at the final
MTA site (e.g.  Postmaster), while multipart/report is of content-type
  message/delivery-status, described in section 2.1 of this document.

+ If the envelope sender address original message or a portion of the
DSN message is set up to ensure that no delivery status reports will be issued
in response returned
  to the DSN itself.  (For example, in SMTP, sender, it appears as the MAIL FROM
address should be an empty string.) third compoment 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 which contain the same equivalent
  information.  In particular, it is very desirable to preserve the
  subject, date, and message-id (or equivalent) fields from the original
  message.

The message/delivery-status content-type is defined as follows:

     MIME type name: DSN MUST be addressed (in both the message
     MIME subtype name:             delivery-status
     Optional parameters:           none
     Encoding considerations:       "7bit" encoding is sufficient header and
                                    should be used the transport
envelope) to maintain
                                    readability when viewed by non-MIME
                                    mail readers.
     Security considerations:       discussed in section 6 of this memo.

The message/delivery-status report type the return address from the transport envelope which
accompanied the original message for use which the DSN was generated.  (For
a message that arrived via SMTP, the envelope return address appears in
the multipart/report
is "delivery-status". MAIL FROM command.)

The body of a message/delivery-status consists From field of one or more "fields"
formatted according to the ABNF of RFC 822 message header "fields" (see [5]).
The per-message fields appear first.  Following the per-message fields
are one or more groups of per-recipient fields.   Each group the DSN SHOULD contain the
address of per-
recipient fields a human who is preceded by responsible for maintaining the mail system at
the Reporting MTA site (e.g.  Postmaster), so that a blank line.  Using reply to the ABNF of RFC
822, DSN
will reach that person.  Exception: if a DSN is translated from a
foreign delivery report, and the syntax gateway performing the translation
cannot determine the appropriate address, the From field of the message/delivery-status content is as follows:

     delivery-status-content =
         per-message-fields 1*( CRLF per-recipient-fields )

These fields are described in detail below.  Note: Since these fields
are defined according to DSN MAY
be the rules address 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 TAB.  Text which appears in parenthesis human who is considered a comment
and not part of responsible for maintaining the contents
gateway.

The envelope sender address 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 SHOULD be chosen to ensure that



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fields may use the "encoded-word" construct defined January 1995



no delivery status reports will be issued in [6].

Several fields exist response to identify the "MTS type" of the original, final,
or remote MTA.  For the purpose of this specification, a "message
transfer system" (MTS) is a service which transfers electronic DSN itself,
and MUST be chosen so that DSNs will not generate mail
messages from one user (the sender) loops.  (If an
SMTP transaction is used to one or more users (recipients). send a DSN, the MAIL FROM address MUST be an
empty string.)

A particular MTS will have its own protocols DSN describes the delivery status for (a) electronic mail
addresses exactly one message.
However, an MTA MAY report on the delivery status for senders and recipients, (b) names several recipients
of MTAs, (c) the format same message in a single DSN.  Due to the nature of electronic the mail messages, (d) transferring messages and
transport system (where responsibility for message delivery from one MTA to another, and (e)
communicating delivery status conditions.

An MTS-type is of a identifier for a particular message transfer system.  A
registry of MTS-types is maintained by the Internet Assigned Numbers
Authority (IANA).  IANA will not register MTS-type names beginning with
"X-"; these are reserved for experimental use.

The syntax for an MTS-type is:

     mts-type = atom

Because DSNs to its
recipients may be issued for messages that originated in foreign mail
systems, or gatewayed from delivery status reports that were issued in
foreign mail systems, many of the address split among several MTAs, and status codes fields delivery to any
particular recipient may be delayed), multiple DSNs may be still be
issued in some format other than that normally used in the Internet. response to a single message submission.


2.1 The
various MTS-type fields are 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
                                    should be used to identify the maintain
                                    readability when viewed by non-MIME
                                    mail system readers.
     Security considerations:       discussed in section 4 of this memo.

The message/delivery-status report type for use in which a
particular address or status code appeared.  For example, if the final-
mts-type multipart/report
is X400, the final-recipient address must be an X.400 recipient
address, and the final-status code must be an X.400-style error code.
Like notification field names, MTS-type names are also case-insensitve.

A number "delivery-status".

The body of DSN fields are defined to have a field body consisting message/delivery-status consists of
"xtext".  Within such fields, one or more "fields"
formatted according to the normal ABNF of RFC 822 special characters header "fields" (see [6]).
The per-message fields appear first, followed by a blank line.
Following the per-message fields are
not used.  Portions one or more groups of "xtext" enclosed in paraenthesis are treated as
comments, but such comments are not considered separators for the
purpose per-recipient
fields.  Each group of lexical analysis.  Except 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 TAB.  Text which appears in



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parenthesis is considered a comment and escaped-crlf's,
all 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 [7].

A number of DSN fields are defined to have a portion of a field body of
"xtext".  "xtext" is used to allow encoding sequences of octets which do
not consist entirely of ASCII characters, and also to allow comments to
be inserted in the data.  Any octet may be represented by "+" followed
by two upper case hexadecimal digits.  With certain exceptions, octets
that correspond to ASCII characters may be represented as themselves.
SPACE and HTAB characters are significant.  RFC 1522 ignored.  Comments may be included by
enclosing them in parenthesis.  Except within comments, encoded-words
such as defined in [7] may NOT be used in xtext.

"xtext" is formally defined as follows:

     xtext = *( xchar / hexchar / escaped-crlf linear-white-space / comment )

     xchar = any ASCII CHAR between SPACE (32) "!" (33) and TILDE "~" (126) inclusive,
          except for "#", "+", "\" and "(".

"hexchar"s are intended to encode octets that cannot be represented as
plain text, either because they are reserved, or because they are non-
printable.  However, any octet value may be represented by a "hexchar".

     hexchar = ASCII "#" "+" immediately followed by two upper case



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          hexadecimal digits

An escaped-crlf may appear at the end of a line to allow the field to be
continued to the next line without inserting any white space.

     escaped-crlf = "\" immediately followed by the characters: CR LF
     SPACE

When encoding a field whose body is defined an octet sequence as "xtext", a SPACE which
immediately precedes a CR LF pair should xtext:

+ Any ASCII CHAR between "!" and "~" MAY be encoded either as a
"hexchar", or itself.  (Some
  CHARs in this range may also be encoded as an "escaped-crlf" followed by a SPACE.

When decoding a field whose body is defined "hexchar"s, at the
  implementor's discretion.)

+ ASCII CHARs that fall outside the range above must be encoded as "xtext", any number of
SPACEs which immediately precede a CR
  "hexchar".

+ Line breaks (CR LF pair (i.e. end of line) should SPACE) MAY be ignored.


3.1 Per-Message inserted as necessary to keep line
  lengths from becoming excessive.

+ Comments MAY be added to clarify the meaning for human readers.


2.1.2 "*-type" subfields

Several DSN Fields

Some fields of require a DSN apply to all of the delivery attempts described by "-type" subfield that DSN.  These fields may appear at most once in any DSN. specifies the format
of a mailbox address, status code, or MTA name.  These
fields types are used to correlate defined
as follows:




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+ An "address-type" specifies the DSN with format of a mailbox address.  For
  example, Internet mail addresses use the original message
transaction and to provide additional information which may be useful to
gateways.

With "rfc822" address-type.

       address-type = atom

+ A "diagnostic-type" specifies the exception format of the original-mts-type a status code.  For
  example, when a DSN field itself, contains a reply code reported via the
  Simple Mail Transfer Protocol [3], the "smtp" diagnostic-type is used.

       diagnostic-type = atom

+ An "MTA-name-type" specifies the format of
each of an MTA name.  For example,
  for an SMTP server on an Internet host, the per-message fields MTA name is specific to the original-mts-type.

     per-message-fields domain
  name of that host, and the "dns" MTA-name-type is used.

       MTA-name-type = [ original-mts-type-field CRLF ]
                          [ original-envelope-id-field CRLF ]
                          final-mts-type-field CRLF
                          final-mta-field CRLF
                          [ received-from-field CRLF ]
                          [ arrival-date-field CRLF ]
                          *( extension-field CRLF )


3.1.1 atom

The Original-MTS-Type field

     original-mts-type-field = "Original-MTS-Type" ":" MTS-type 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 a one or more specifications that provide such
descriptions.  (The "rfc822" address-type, "smtp" diagnostic-type, and
"dns" MTA-name-type are defined in [4].)

The original-mts-type field contains registration for an address-type should include the MTS-type name of the MTS in
which
address-type and a specification (or a reference to a specification)
that describes the syntax for that type of electronic mail address.

The registration for a diagnostic-type should include the message was submitted.  This name MUST be of the
diagnostic-type and a specification that describes the syntax of
diagnostic codes and the meanings of legal values for such codes.

The registration of an IANA-registered
MTS-type name, unless it MTA-name-type should include the name of the MTA-
name-type and a description of the syntax of such names.

IANA will not accept registrations for any address-type, diagnostic-
type, or MTA-name-type name that begins with "X-".

This field is required if  These type names are
reserved for experimental use.


2.1.3 Lexical tokens imported from RFC 822

The following lexical tokens, defined in [6], are used in the original-envelope-id field or any
original-recipient field is present.  If neither of these ABNF
grammar for DSNs: atom, CHAR, comment, CR, CRLF, date-time, DIGIT, LF,
linear-white-space, SPACE.


2.2 Per-Message DSN Fields

Some fields is
present, of a DSN apply to all of the original-mts-type field delivery attempts described by
that DSN.  These fields may be omitted.


3.1.2 The Original-Envelope-Id field appear at most once in any DSN.  These



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The optional original-envelope-id field contains an "envelope
identifier" which uniquely identifies January 1995



fields are used to correlate the transaction during which DSN with the original message was submitted,
transaction and was either (a) to provide additional information which may be useful to
gateways.

     per-message-fields =
          [ original-envelope-id-field CRLF ]
          reporting-mta-field CRLF
          [ received-from-mta-field CRLF ]
          [ arrival-date-field CRLF ]
          *( extension-field CRLF )


2.2.1 The Original-Envelope-Id field

The optional Original-Envelope-Id field contains an "envelope
identifier" which 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.

The original-envelope-id line Original-Envelope-Id field is defined as follows:

     original-envelope-id-field =
          "Original-Envelope-Id" ":" envelope-id

     envelope-id = xtext

There may be at most one original-envelope-id Original-Envelope-Id field per DSN.  If an
original "envelope identifier" is not available when a DSN is issued,
the original-envelope-id Original-Envelope-Id DSN field MUST SHOULD NOT be included in the DSN.

NOTE IN DRAFT: This last sentence may be a bit too strong.  The intent
is to prevent an

NOTE: An MTA from simply concocting should not supply an envelope-id for a
message. message if one was
not present in the transmission envelope.  For the envelope-id field to
be useful, it must be unique for each message transmission, known by the
sender of the original message when the message was sent, and be
transmitted along with the message envelope.  However, the MTA issuing
the DSN has no way of knowing whether the envelope-id it received in a
message envelope is the same as the "original" one known by the message
sender.  Some mail protocols require an envelope-id or similar token,
and a gateway into such an
environemnt environment will have to concoct one without
the sender's knowledge.  If a DSN is issued for such a message, it will may
contain an envelope-id which is not specified by the sender.  In general
this seems unavoidable.

The envelope-id is NOT case-insensitive.  The DSN must preserve the
original case and spelling of the envelope-id.





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NOTE: The original-envelope-id Original-Envelope-Id is NOT to be confused with the message-id same as the Message-Id from
the message header.  The message-id Message-Id identifies the content of the
message, while the original-envelope-id Original-Envelope-Id identifies the transaction in
which the message is sent.


3.1.3


2.2.2 The Final-MTS-Type Reporting-MTA DSN field

     final-mts-type-field

     reporting-mta-field = "Final-MTS-Type"
          "Reporting-MTA" ":" MTS-type mta-name-type ";" mta-name

     mta-name = xtext

The final-mts-type Reporting-MTA field contains the name of the MTS via which the
message arrived at the final MTA.  The MTS-type MUST be registered with
IANA, unless it begins with "X-".

NOTE WELL: If the final MTA is actually a multi-protocol MTA or mail
gateway, the final-mts-type is defined as follows:

A DSN describes the name results of the MTS by which the attempts to deliver, relay, or gateway a
message



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ARRIVED at that MTA. to one or more recipients.  The final-mts-type field Reporting-MTA is REQUIRED.


3.1.4 The Final-MTA DSN field

     final-mta-field = "Final-MTA" ":" xtext

The final-mta field contains the name of the MTA which issued
attempted to perform the delivery, relay, or gateway operation described
in the DSN.  This field is REQUIRED.

This required.

Note that the Reporting-MTA is not necessarily the MTA which reported actually
issued the success or failure of
a delivery attempt. DSN.  For example, if example:

+ 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 final-mta Reporting-MTA field.

The contents of the final-mta field are formatted according

+ If an attempt to the
conventions deliver a message outside of the "final" MTS, as indicated by Internet resulted in
  a nondelivery notification which was gatewayed back into Internet
  mail, the final-mts-type
field. 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.

The mta-name portion of the Reporting-MTA field is formatted according
to the conventions indicated by the mta-name-type subfield.

Because the exact spelling of an MTA name may be significant in a
particular environment, MTA names must be considered case-sensitive.


3.1.5


2.2.3 The Received-From Received-From-MTA DSN field

The optional Received-From Received-From-MTA field indicates the name of the MTA from
which the message was received.  (In Figure 1, this MTA is labelled labeled the
"penultimate"
"preceding" MTA.)

     received-from-field

     received-from-mta-field = "Received-From"
          "Received-From-MTA" ":" xtext mta-name-type ";" mta-name

If the message was received from an Internet host, the contents of the
Received-From field



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mta-name subfield should be the Internet domain name corresponding to
the network address of that host.  Otherwise, the contents of  (In this field case, the mta-name-type will
usually be "smtp", but may be any printable string identifying the MTA from which the message different if another protocol was received. used.)

The contents mta-name portion of the received-from Received-From-MTA field are is formatted
according to the conventions of the "final" MTS, as indicated by the final-mts-type
field. mta-name-type subfield.

Since case is significant in some mail systems, the exact spelling,
including case, of the MTA name should be preserved.


3.1.6


2.2.4 The Arrival-Date DSN field

The optional Arrival-Date field indicates the date and time at which the
message arrived at the final Reporting MTA.  If the Date field is also
provided in a per-recipient field, this can be used to determine the
interval



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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.  Numeric
timezones ([+/-]HHMM format) MUST be used.


3.1.7 Extension fields

Additional per-message DSN fields may be defined in the future, if
necessary to tunnel MTS-specific delivery for a particular MTS-type or
by any extension to this memo which is published as an RFC.

     extension-field = extension-field-name ":" xtext

     extension-field-name = atom


3.2


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.

The syntax for the group of per-recipient fields is as follows:


     per-recipient-fields = basic-fields mts-specific-fields

     basic-fields =         recipient-field CRLF
                            action-field CRLF
                            status-field CRLF
                            [ date-field CRLF ]
                            [ final-log-id-field CRLF ]
                            [ expiry-date-field CRLF ]

     mts-specific-fields =
          [ original-recipient-field CRLF ]
                            [
          final-recipient-field CRLF ]
                            [ final-status-field
          action-field CRLF
          status-field CRLF ]
          [ remote-mts-type-field remote-mta-field CRLF ]
          [ remote-mta-field diagnostic-code-field CRLF ]
          [ remote-recipient-field last-attempt-date-field CRLF ]
          [ remote-status-field expiry-date-field CRLF ]
          *( extension-field CRLF )


2.3.1 Original-Recipient field

The "basic" fields are generic in nature and are always defined
according to Internet mail conventions.  Except for Original-Recipient field indicates the "date" field,
these fields are required for each original recipient listed in a DSN.  When mts-
specific fields are either not available or not usable (say, address as
specified by a
gateway to a different environment), the "basic" fields provide fallback sender of the message for which the DSN is being
issued.



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values with a known syntax.

The syntax of each mts-specific field is specific to the mts-type for
which that January 1995



     original-recipient-field =
          "Original-Recipient" ":" address-type ";" generic-address
     generic-address = xtext

The address-type field applies.  For example, indicates the format type of the final-
recipient, final-mta, original recipient
address.  If the message originated within the Internet, the address-
type field field will normally be "rfc822", and final-status fields are given by the final-
mts-type field.

This combined approach allows "foreign" information to address will be preserved in
DSNs for messages that are gatewayed
according to the syntax specified in or out of [6].  The value "unknown" should be
used if the Internet, while
retaining a set Reporting MTA cannot determine the type of "canonical" information which will always the original
recipient address from the message envelope.

This field is optional.  It should be present, included only if the sender-
specified recipient address was present in the message envelope, such as
by the ESMTP extensions defined in [4].  This address is the same as
that provided by the sender and which can provide minimum functionality.


3.2.1 Basic per-recipient fields


3.2.1.1 Recipient be used to automatically correlate
DSN reports and message transactions.


2.3.2 Final-Recipient field

The Recipient Final-Recipient field indicates the recipient for which this set of per-
recipient
per-recipient fields applies.  This field MUST be present is required in each set of
per-recipient data.

The syntax of the field is as follows:

     recipient-field

     final-recipient-field = "Recipient"
          "Final-Recipient" ":" [route] addr-spec address-type ";" generic-address

The value following address subfield of the Recipient recipient field contains should contain the RFC 822 mailbox
address of the recipient address. (from the transport envelope) as it was when
the message was accepted for delivery by the Reporting MTA.

The Final-Recipient address MUST be in RFC 822 "addr-spec"
format (with an optional "route" prefix), and MUST contain the fully-
qualified domain name of may differ from the recipient's domain.

(EXCEPTION: If address originally
provided by the DSN is being issued for this recipient, sender, because of it may have been transformed during
forwarding and gatewaying into an
improperly formatted address or incomplete domain name, totally unrecognizable mess.
However, in the recipient
DSN absence of the optional Original-Recipient field, the
Final-Recipient field and any returned content may contain be all the illegal address or the address with
information available to correlate the
incomplete domain name.)

NOTE IN DRAFT:  There is a conflict here between having a "failed" DSN
report exactly the conditions that cause an error, or having with a
rigorously formatted particular message
submission.

The address-type field that contains the failed address (even if the
problem is masked when indicates the type of address is reformatted).  To this author
(KM), the former goal seems more important.  Delivery failure is often
caused expected by bad address rewriting, and the portion of an
reporting MTA in that
generates a DSN can hardly be expected to context; for example, recipient addresses
obtained via SMTP will normally be better at such rewriting
(while attempting to translate a foreign address into 822 syntax) than
the portion of the MTA that rewrites such addresses for the message
envelope. address-type "rfc822".

NOTE: The best way Reporting MTA is not expected to solve ensure that the address rewriting problem would
seem to be
actually conforms to make the source syntax conventions of the problem obvious via accurate error
reporting using DSNs.

NOTE:  Although RFC 1123 [7] discourages explicit source routing address-type.
Instead, it should report exactly the address received in
SMTP, and allows SMTPs to route directly the
envelope, without any changes other than those needed to encode the final domain, source
address in "xtext".




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routes are still allowed.

If January 1995



Since mailbox addresses (including those used in the recipient address as originally specified is available Internet) may be
case sensitive, the case of alphabetic characters in RFC 822
addr-spec format, the Recipient address must
be preserved.



2.3.3 Action field should contain that address.
Otherwise, the Recipient

The Action field should contain indicates the closest available
recipient address to that specified action performed by the sender, as expressed in RFC
822 addr-spec format.

This address may not correspond to the address Reporting-MTA
as originally sent
because it may have been transformed during forwarding and gatewaying
into an totally unrecognizable mess.  In the absence a result of its attempt to deliver the optional
original-recipient field, the Recipient field and any returned content
may be all the information available to correlate the DSN with a
particular message transaction.

Although domain names are case-insensitive, the case of alphabetic
characters in the local-part of the addr-spec must be preserved.


3.2.1.2 action field

The action field indicates the reason the DSN was issued. 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" "failure" / "delayed" / "delivered" / "relayed"

The action-value may be spelled in any combination of upper and lower
case characters.

"failed"

"failure"    indicates that the message could not be delivered to the
             recipient.  The final Reporting MTA has abandoned any attempts to
             deliver the message to this recipient.  No further
             notifications should be expected.

"delayed"    indicates that the final 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 expander.  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.




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"relayed"    indicates that the message has been relayed or gatewayed
             into an a "foreign" environment that does not accept
             responsibility for generating DSNs according to this
             specification.  Additional notification messages may be
             provided by the
             "remote" "foreign" environment that may or may not
             conform to this specification.  (However, for subsequent
             notifications, the
             'original-recipient' field Original-Recipient and Original-
             Envelope-ID fields will almost certainly not be included
             because it they will no longer be available.)





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NOTE ON ACTION VS. STATUS CODES:  Although the 'action' field appears might seem
to be redundant with the 'status' field, this is not the case.  In
particular, a 4XX "temporary failure" ("4") status value code could be used with
an action-value of either "delayed" or "failed".


3.2.1.3 status "failure".


2.3.4 Status field

The per-recipient status Status field contains a transport-independent status
code which 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 = 3*DIGIT

"status" uses DIGIT "." 1*DIGIT "." 1*DIGIT

Status codes thus consist of three numerical fields separated by ".".
The first sub-field indicates whether the set delivery attempt was
successful (2 = success, 4 = persistent temporary failure, 5 = permanent
failure).  The second sub-field indicates the probable source of reply codes from SMTP [3] any
delivery anomalies, and its extensions
([8], [9]), with additions to support indication of error conditions
that can never result from an SMTP dialogue.  If an SMTP reply code is
not available, the closest match should third sub-field denotes a precise error
condition.

DSN status codes must be chosen from either defined by standards track RFCs.  IANA will
maintain a registry of such codes.

Initially, the following three status codes are defined:

     2.0.0  successful relay, gateway, or delivery operation
     4.0.0  unspecified persistent temporary failure
     5.0.0  unspecified permanent failure

NOTE: An extensive set of
SMTP reply status codes or is currently under development
(see [5]) which, if approved for standardization, will supplement the additional codes listed in an appendix.
list above.  Eventually the list may be incorporated into a future
version of this memo.

Although status-codes are purely numeric, explanatory text may be
included as a comment in parentheses following the status-code.

NOTE:  These "new" codes should only appear in delivery status
notifications.


2.3.5 Remote-MTA field

The creation of "new" status-codes for delivery status
notifications DOES NOT extend value associated with the legal set of reply codes to be used
with the SMTP protocol.

The structure of Remote-MTA DSN status-codes is described in an appendix to this
memo.


3.2.1.4 date field

The "date" field gives the date and time of the last delivery attempt
(whether successful or unsuccessful) by the final MTA.  Note that this
may not should be a printable
ASCII representation of the same as the date header field name of the message used to
transmit this "remote" MTA that reported
delivery status notification.  In cases where to the DSN was "reporting" MTA.




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generated by a gateway, the RFC 822 header will contain the time the
message was sent and the DSN date field should be the time the
notification event occurred.

     date-field January 1995



     remote-mta-field = "Date" "Remote-MTA" ":" date-time mta-name-type ";" mta-name

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 SHOULD 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 no remote MTA was
involved in RFC 822 'date-time' format.  Numeric
timezones ([+/-]HHMM format) MUST be used.


3.2.1.5 final-log-id field

The "final-log-id" field gives the final-log-id attempted delivery 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" ":" xtext

This field is optional.


3.2.1.6 expiry-date recipient.


2.3.6 Diagnostic-Code field

For DSNs of type "delay", a "failure" or "delayed" recipient, the "expiry-date" Diagnostic-Code DSN field gives
contains the date after
which actual diagnostic code issued by the final MTA expects to abandon all attempts mail transport.  Since
such codes vary from one mail transport to deliver another, the
message diagnostic-type
subfield is needed to that recipient.

     expiry-date-field specify which type of diagnostic code is
represented.

     diagnostic-code-field = "Expiry-Date" "Diagnostic-Code" ":" date-time diagnostic-type ";"
          xtext

NOTE:  The date and time are expressed information in RFC 822 'date-time' format.  Numeric
timezones ([+/-]HHMM format) MUST be used.


3.2.2  MTS-specific Per-recipient fields

NOTE:  Unless otherwise stated, the syntax for a MTS-specific Per-
recipient Diagnostic-Code field is:

     mts-specific-field = field-name ":" xtext

This reflects the ability to carry any kind of addresses, MTA names, or
status codes.  A particular MTS-type may place restrictions on the
allowable values for MTS-specific fields when be somewhat
redundant with that MTS-type is used.

With from the exception of MTS-type fields, all MTS-specific fields are case
sensitive. Status field.  The final-MTA must not change the case Status field is needed
so that any DSN, regardless of origin, may be understood by any values
reported in these fields.



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3.2.2.5 original-recipient field

The "original-recipient" code will sometimes
be less precise than the actual transport diagnostic code, the
Diagnostic-Code field indicates is provided to retain the original recipient address
as specified by latter information.
Such information may be useful in a trouble ticket sent to the sender
administrator of the message for which the DSN is being
issued. Reporting MTA, or when tunneling foreign
nondelivery reports through DSNs.

If the message originated outside of Diagnostic Code was obtained from a Remote MTA during an attempt
to relay the Internet, message to that MTA, the original-
recipient Remote-MTA field will not necessarily contain an RFC 822-style recipient
address.  However, if should be
present.  When interpreting a DSN, the original-mts-type presence of a Remote-MTA field is present,
indicates that the
original-recipient address MUST conform to Diagnostic Code was issued by the conventions Remote MTA.  The
absence of a Remote-MTA indicates that the Diagnostic Code was issued by
the
original-mts-type. Reporting MTA.

This field is optional.  It 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 only if transport-specific
diagnostic information is available.


2.3.7 Last-Attempt-Date field

The Last-Attempt-Date field gives the sender-
specified recipient address was present in the message envelope, such as
by the ESMTP extensions defined in [4].  This address is the same as
that provided by the sender and can be used to automatically correlate
DSN reports date and message transactions.


3.2.2.6 final-recipient field

The final-recipient field contains the electronic mail address time of the
recipient at the time last attempt
to relay, gateway, or deliver the message was accepted for delivery (whether successful or
unsuccessful) by the final Reporting MTA.  This field is optional.

If not necessarily the final-mts-type field is present, same as
the syntax value of the final-
recipient field MUST conform to the syntax for that MTS-type.


3.2.2.7 final-status Date field

The value associated with from the final-status DSN field should be a
printable ASCII representation header of a MTS-specific status code that
indicates the final MTA's precise reason for the success or failure to message used to
transmit this recipient.  The possible values for this field are specific to delivery status notification: In cases where the final-mts-type.

This field is optional.


3.2.2.8 remote-mts-type field

The value associated with remote-mts-type DSN field is the MTS type of was
generated by a gateway, the "remote" MTA, as defined in section 2 of this document.

This Date field is optional.  It SHOULD NOT be included if no remote MTA was
involved in the attempted delivery of the message to that recipient.


3.2.2.9 remote-mta field header should



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The value associated with January 1995



contain the time the DSN was sent by the gateway and the remote-mta DSN Last-
Attempt-Date field should be a printable
ASCII representation of the name of time the "remote" MTA that reported last delivery status to the "final" MTA.

NOTE: The remote-mta field preserves the "while talking to" information
that was provided in some pre-existing non-delivery reports. attempt
occurred.

     last-attempt-date-field = "Last-Attempt-Date" ":" date-time

This field is optional.  It SHOULD NOT be included if no remote MTA was
involved in the attempted delivery of the message to that recipient.

The conventions for the name actual date
and time of the remote-mta field last delivery attempt are specific to the
remote MTS-type.


3.2.2.10 remote-recipient field

The value associated with the remote-recipient DSN field should not available (which might be a
printable ASCII representation of
the recipient address as presented to case if the "remote" MTA in an attempt DSN were being issued by the "final" MTA to relay the message. a gateway).

The conventions of the remote-recipient address date and time are specific to the
remote MTS-type.

This field is optional.  It SHOULD NOT expressed in RFC 822 'date-time' format.  Numeric
timezones ([+/-]HHMM format) MUST be included if its value is the
same as that of the final-recipient DSN field.


3.2.2.11 remote-status field

The value associated with the remote-status DSN used.


2.3.8 Expiry-Date field should be a
printable ASCII representation

For DSNs of type "delay", the status value returned by "Expiry-Date" field gives the
remote MTA to date after
which the final Reporting MTA in response expects to the final MTA's attempt abandon all attempts to
relay deliver the
message to the remote MTA. that recipient.  The conventions for interpreting the remote-status DSN field are
specific to the remote MTS-type.

This Expiry-Date field is optional, because some mail systems supply no additional
information beyond that which is returned optional for
"delay" DSNs, and SHOULD NOT appear in the 'action' other DSNs.

     expiry-date-field = "Expiry-Date" ":" date-time

The date and 'status'
fields.


3.2.2.12 time are expressed in RFC 822 'date-time' format.  Numeric
timezones ([+/-]HHMM format) MUST be used.


2.4 Extension fields

Per-recipient extension

Additional per-message or per-recipient DSN fields may also be defined, using defined in the same
syntax
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 per-message extension field.


4. Extension Mechanism for DSNs

The experimental use.  DSN body part includes several extensible fields.  The extensible
fields are:



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(a) New Status Codes

New status codes may be defined to reflect error conditions which are
not covered either by existing SMTP reply codes or by the additional
codes defined in section 10.1 of this memo.  New codes must be
consistent
field names NOT beginning with the theory of status codes defined in section 10, and "X-" MUST be defined in a published in an RFC.

NOTE IN DRAFT: I (KM) am leaving this section as-is until the WG gets
consensus on whether to define a new status code scheme or extend the
existing SMTP scheme.

(b) New MTS types

New MTS-type names may

Extension DSN fields MAY also be defined to allow for the carriage of following reasons:

+ To allow additional information from foreign
address and delivery status code information in mts-specific DSN fields.  New
MTS-types must reports
  to be defined in a published RFC, which ideally should
include a complete specification for exchanging mail between the tunneled through Internet and the foreign MTS-type.

At a minimum, the definition DSNs.  The names of an additional MTS-type such DSN fields
  should include:

(1) begin with an indication of the proposed MTS-type foreign environment name
(2) (e.g.
  X400-Physical-Forwarding-Address).

+ To allow the syntax transmission of addresses for that MTS-type, as they are diagnostic information which is specific
  to be
    represented in DSN fields
(3) the syntax of MTA names for that MTS-type
(4) the syntax of status codes for that MTS-type, along with a list of
    the codes that are valid

NOTE:  A definition for the INTERNET MTS-type appears in section 11 particular mail transport protocol.  The names of
this memo.

(c) New DSN Fields

Additional per-message or per-recipient such DSN fields may be defined by any
extension to this memo that is published as
  should begin with an RFC.  These indication of the mail transport being used (e.g.
  SMTP-Remote-Recipient-Address).  Such fields should be used for
  diagnostic purposes only to contain additional information needed to tunnel and not by user agents or
report mail gateways.

+ To allow transmission of diagnostic information from foreign systems.  In the event the DSN fields
defined in this memo are insufficient for reporting delivery attempts in
Internet mail, this specification as a whole should be revised.

Extension field names that are which is specific to a
  particular MTS-type message transfer agent (MTA).  The names of such DSN fields
  should begin with an indication of the MTS-type name and a hyphen. For example: a field called
"X400-Remote-MTA-Brain-Death" would be specific to MTA which produced the "X400" MTS-type.

Extension field names beginning with "X-" are reserved for experimental
use.


5. Conformance and Usage Requirements DSN.



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  (e.g. Foomail-Queue-ID).

MTA implementors 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 which 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 MTA name should follow the "X-", (e.g.  "X-Foomail-
Log-ID").

All extension fields are assumed to have the following syntax:

     extension-field = extension-field-name ":" xtext

     extension-field-name = atom


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 [4]), it is sufficient that delivery failure reports use this
protocol.

A minimal implementation of this specification will need generate only the
Recipient,
Reporting-MTA per-message field, and the Final-Recipient, Action, and
Status fields.  However, generation fields for each attempt to deliver a message to a recipient
described by the DSN.  Generation of the other
fields fields, when appropriate,
is strongly recommended.

MTAs and gateways MUST NOT generate the "original-recipient" Original-Recipient field of a
DSN unless the mail transfer protocol ensures that provides the address provided
is the one originally
specified by the sender at the time of submission. (Ordinary SMTP does
not make that guarantee, but the SMTP extension defined in [4] 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" "failure" DSN for that recipient.  If a DSN is requested
for a message that is forwarded to multiple recipients, the forwarding
MTA should normally issue a "relayed" DSN for the originally-specified
recipient and not propagate the request for a DSN to the forwarding
addresses.  Alternatively, the forwarding MTA can relay the request for
a DSN to exactly one of the forwarding addresses and not propagate the
request to the others.

Submission of a message to a mailing list exploder is considered final



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delivery of the message.  Upon delivery of a message to a recipient
address corresponding to a mailing list expander, the final 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 Appendix 14.) section 10.)

This specification places no restrictions on the processing of DSNs
received by user agents or distribution lists.


6.


4. Security considerations

The following security considerations apply when using DSNs:


6.1


4.1 Forgery



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DSNs may be forged as easily as ordinary Internet electronic mail.  User
agents and automatic mail handling facilities (such as mail distribution
list expanders) 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 receipt sending of:

+ A falsified delivery notification when the message as is not delivered, delivered to
  the indicated recipient,
+ A falsified non-delivery notification when the message was delivered, in fact
  delivered to the indicated recipient,
+ A falsified final recipient Final-Recipient address,
+ A falsified remote-mta Remote-MTA identification,
+ A falsified relay notification when the message is "dead ended".
+ Unsolicited DSNs


6.2


4.2 Confidentality

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 messaes 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.



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MTA authors are encouraged to provide a mechanism which enables the end
user to preserve the confidentality 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)

a. issuing a "relayed" DSN (if a positive DSN were requested) when a
   message were forwarded to a confidential forwarding address, and
   disabling requests for positive DSNs for the forwarded message,
b)

b. omitting the "remote-*" "Remote-*" or extension fields of a DSN whenever they would
   otherwise contain confidential information (such as a confidential
   forwarding address,
c) address),

c. for messages forwarded to a confidential address, setting the
   envelope return address (e.g. SMTP MAIL FROM address) to the empty
   string (so that no DSNs could would be issued), sent from a downstream MTA to the
   original sender),

d. for messages forwarded to a confidential address, disabling delivery
   notifications for the forwarded message (e.g. if the "next-hop" MTA
   using ESMTP and supports the DSN extension, by using the NOTIFY=NEVER
   parameter to the RCPT command), or
d)

e. 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 it were the originator.  After
   obtaining final delivery status, it would issue a "proxy" DSN to the
   original sender.


6.3
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.

Implementors are cautioned that many existing MTAs will send nondelivery
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
"failure" DSN can not be relied upon as a guarantee that a message was



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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.  If one of those
delivery attempts succeeds and the other one fails, a "failure" DSN
could be issued even though the message actually reached the recipient.


7.


5. Acknowledgments

The authors wish to thank the following people for their reviews of
earlier drafts of this document and their suggestions for improvement:
Eric Allman, Harald Alvestrand, Allan Cargille, Jim Conklin, Peter
Cowen, Dave Crocker, Ned Freed, Steve Kille, John Klensin, John Gardiner
Myers, Mark Nahabedian, Julian Onions, Jacob Palme, Jean Charles Roy,
and Gregory Sheehan.


8.


6. References

[1] Borenstein, N., Freed, N. "Multipurpose Internet Mail Extensions",
    RFC 1521, Bellcore, Innosoft, September 1993.

[2] Moore, K., Vaudreuil, G. "Multipart/Report", Internet-Draft.

[3] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
    USC/Information Sciences Institute, August 1982.

[4] Moore, K.  "SMTP Service Extension for Delivery Status
    Notifications", Internet-Draft.

[5] Vaudreuil, G.  "Enhanced Mail System Status Codes", Internet-Draft.

[6] Crocker, D., "Standard for the Format of ARPA Internet Text
    Messages", STD 11, RFC 822, UDEL, August 1982.

[6]

[7] Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part Two:
    Message Header Extensions for Non-Ascii Text", RFC 1522, University
    of Tennessee, September 1993.

[7] Braden, R.  "Requirements for Internet Hosts - Application and
    Support" RFC 1123, October 1989.

[8] Klensin, J., Freed, N., Rose, M., Stefferud, E., Crocker, D.  "SMTP
    Service Extensions" RFC 1651, MCI, Innosoft International, Inc.,
    Dover Beach Consulting, Inc., Network Management Associates, Inc.,
    Silicon Graphics, Inc,


7. Author's Addresses

Keith Moore
University of Tennessee
107 Ayres Hall



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[9] Klensin, J., Freed, N., Moore, K.  "SMTP Service Extension for
    Message Size Declaration" RFC 1653, MCI, Innosoft International,



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    Inc., University of Tennessee, July 1994.


9. Author's Addresses

Keith Moore
University of Tennessee
107 Ayres Hall January 1995



Knoxville, TN 37996-1301
USA
email: moore@cs.utk.edu

Gregory M. Vaudreuil
Octel Network Services
17080 Dallas Parkway
Dallas, TX 75248-1905
USA
email: Greg.Vaudreuil@Octel.Com












































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10. January 1995



8. Appendix - Theory of status-codes collected grammar

NOTE:  The first digit of the status-code is following lexical tokens are defined as follows:

2yz  Positive Completion status

     Final delivery of the message has been successfully completed.

4yz  Transient Negative Completion status

     Attempts to deliver the message have been abandoned because of the
     persistence of "transient" failures.  However, the error condition
     appears to be temporary and the sender may wish to resend the
     message.

     In SMTP, 4yz reply codes indicate conditions where the SMTP client
     is allowed to "try again later" to deliver a message.  However, if
     delivery attempts continue in RFC 822:  atom, CHAR,
comment, CR, CRLF, date-time, DIGIT, LF, linear-white-space, SPACE.

action-field = "Action" ":" action-value

action-value = "failure" / "delayed" / "delivered" / "relayed"

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 ";" xtext

envelope-id = xtext

expiry-date-field = "Expiry-Date" ":" date-time

extension-field = extension-field-name ":" xtext

extension-field-name = atom

final-recipient-field =
     "Final-Recipient" ":" address-type ";" generic-address

generic-address = xtext

; "hexchar"s are used to fail, eventually the client will
     "give up". At this the client should issue a DSN. The last 4yz
     reply code obtained from the SMTP server should encode octets that cannot be reported represented
; as the
     status-code.

5yz  Permanent Negative Completion status

     The message could not be delivered plain text, either because of some permanent error
     associated with the recipient address.  The sender should not
     attempt to resend the message to that recipient.

6yz  Indeterminate Completion status

     This group of status codes is used when a message is relayed they are reserved, or
     gatewayed into a mail system from which any requested DSNs may not
     be returned.  No further notifications should be expected for this
     message and recipient.  However, because
; they may be issued, perhaps with
     incomplete information.

The second digit of the are non-printable.

hexchar = ASCII "+" immediately followed by two upper
     case hexadecimal digits

last-attempt-date-field = "Last-Attempt-Date" ":" date-time

mta-name = xtext

mta-name-type = atom

original-envelope-id-field =
     "Original-Envelope-Id" ":" envelope-id

original-recipient-field =
     "Original-Recipient" ":" address-type ";" generic-address

per-message-fields =



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     [ original-envelope-id-field CRLF ]
     reporting-mta-field CRLF
     [ received-from-mta-field CRLF ]
     [ 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 ]
     [ expiry-date-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 is defined as follows:

x0z  Syntax

     These replies refer to syntax errors, syntactically-correct
     commands that don't fit = DIGIT "." 1*DIGIT "." 1*DIGIT

status-field = "Status" ":" status-code

diagnostic-type = atom

xchar = any functional category, ASCII CHAR between "!" (33) and unimplemented
     or superfluous commands.

x2z  Connections

     These replies refer to the transmission channel.

x5z  Mail system

     These replies indicate the status of the receiver mail system vis- "~" (126) inclusive,
     except for "+", "\" and "(".

xtext = *( xchar / hexchar / linear-white-space / comment )



















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     a-vis the requested transfer or other mail system action.

x6z  External servers

     These replies indicate January 1995



     9. Appendix - Guidelines for gatewaying DSNs

     NOTE:  This section provides non-binding recommendations for the status
     construction of any external servers mail gateways that are
     not an integral part of wish to provide semi-transparent
     delivery reports between the Internet and another electronic mail system but whose operation is
     necessary
     system.  Specific DSN gateway requirements for the correct delivery of mail.

The third digit of the status-code gives a finer gradation particular pair of meaning.


10.1 New status-codes for DSNs

In addition to the reply codes
     mail systems may be defined for SMTP, by other documents.


     9.1 Gatewaying from other mail systems to DSNs

     A mail gateway may issue a DSN to convey the following codes contents of a
     "foreign" delivery or non-delivery notification over Internet mail.
     When there are
usable appropriate mappings from the foreign notification
     elements to DSN fields, the information may be transmitted in those
     DSN fields.  Additional information (such as status-codes might be useful in DSNs:

400  Unspecified temporary failure

     This code is a "fallback"
     trouble ticket or needed to tunnel the foreign notification through
     the Internet) may be used when translating temporary
     failure codes from defined in extension DSN fields.  (Such fields
     should be given names that identify the foreign mail systems, when no more precise
     status-code is available.

426  Temporary communications failure

     This code indicates a "temporary" failure to establish
     communications with a host or network protocol, e.g.
     X400-* for which communications is
     necessary X.400 NDN or DN protocol elements)

     The gateway must attempt to deliver supply reasonable values for the message.  Such failures would include
     "host unreachable", "network unreachable",
     Reporting-MTA, Final-Recipient, Action, and "connection refused"
     codes.

466  Temporary routing lookup failure

     This code indicates a "temporary" failure to locate information
     necessary to route a message.  Such failures would include
     unanswered Domain Name Server queries, Status fields.  These
     will normally be obtained by translating the values from the remote
     delivery or other queries non-delivery notification into their Internet-style
     equivalents.  However, some loss of database
     servers that are necessary to route a message.

500  Unspecified permanent failure

     This code information is a "fallback" to be used when translating permanent
     failure codes 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 mail systems when no better status-code
     is available.

601  Message relayed; expect no further notifications

     This system.  The gateway should assign the most precise code is issued for messages for
     which a positive DSN was
     requested but which were successfully relayed or gatewayed into an
     environment which does not support such notifications.






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11. Appendix - definition of describes the INTERNET MTS-type

The INTERNET MTS-type is hereby defined to refer to what is commonly
known failure condition, falling back on "generic"
     codes such as Internet mail.  This includes all electronic mail systems which
(a) use 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 RFC 822 and/or MIME protocols Diagnostic-Code field (with an
     appropriate diagnostic-type value) for the message content, (b) use RFC 822-style sender and in trouble tickets or
     tunneling.

     The sender-specified recipient addresses address, and the original envelope-
     id, if present in their envelopes,
with domains registered the foreign transport envelope, should be
     preserved in the Internet domain name system (DNS)
(including domains registered under "wildcard" mail exchanger (MX)
records), Original-Recipient and (c) exchange such messages with Original-Envelope-ID
     fields.  NOTE: While the IP-connected Internet.
The INTERNET MTS gateway is not limited required to those systems using SMTP.

MTS-type-name: INTERNET

Address-syntax: Addresses for the INTERNET MTS must ensure that
     these fields be in the "addr-
spec" format defined in RFC 822 (with an optional "route" prefix), using
fully-qualified domain names which are registered with the DNS.

MTA-name-syntax:  An INTERNET MTA-name shall authentic, they should be supplied only if there is
     a reasonable chance that the fully-qualified
domain name field values correspond to those at
     the time of submission of the original message.

     The gateway should also attempt to preserve the "final" recipient
     addresses and MTA issuing names from the DSN.  The address Postmaster@{mta-
name} must be a valid address by which foreign system.  In the maintainer interest
     of that MTA human readability, it may be
reached.

Status-codes: Status codes for the INTERNET MTS consist of three decimal
digits.  The initial set of status codes consists of the desirable to encode foreign
     protocol elements as meaningful printable ASCII strings, rather
     than encoding the set of SMTP
reply codes (including those defined by SMTP extensions), along with the
additional codes defined in appendix 10 of this memo.




























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12. Appendix - collected grammar

delivery-status-content =
    per-message-fields *( CRLF per-recipient-fields )

per-message-fields = [ original-mts-type-field CRLF ]
                     [ original-envelope-id-field CRLF ]
                     [ final-mts-type-field CRLF ]
                     final-mta-field CRLF
                     [ received-from-field CRLF ]
                     [ arrival-date-field CRLF ]
                     *( extension-field CRLF )

original-mts-type-field = "Original-MTS-Type" ":" mts-type

original-envelope-id-field = "Original-Envelope-Id" ":" envelope-id

envelope-id = xtext

final-mts-type-field = "Final-MTS-Type" ":" mts-type

final-mta-field = "Final-MTA" ":" xtext

arrival-date-field = "Arrival-Date" ":" date-time

extension-field = extension-field-name ":" xtext

extension-field-name = atom

per-recipient-fields = basic-fields mts-specific-fields

basic-fields =         recipient-field CRLF
                       action-field CRLF
                       status-field CRLF
                       [ date-field CRLF ]
                       [ final-log-id-field CRLF ]
                       [ expiry-date-field CRLF ]

mts-specific-fields =  [ original-recipient-field CRLF ]
                       [ final-recipient-field CRLF ]
                       [ final-status-field CRLF ]
                       [ remote-mts-type-field CRLF ]
                       [ remote-mta-field CRLF ]
                       [ remote-recipient-field CRLF ]
                       [ remote-status-field CRLF ]
                       *( extension-field CRLF )

recipient-field = "Recipient" ":" [route] addr-spec

action-field = "Action" ":" action-value




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status-field = "Status" ":" status-code

date-field = "Date" ":" date-time

final-log-id-field = "Final-Log-ID" ":" xtext

expiry-date-field = "Expiry-Date" ":" date-time

original-recipient-field = "Original-Recipient" ":" xtext

final-recipient-field = "Final-Recipient" ":" xtext

final-status-field = "Final-Status" ":" xtext

remote-mts-type-field = "Remote-MTS-Type" ":" mts-type

remote-mta-field = "Remote-MTA" ":" xtext

remote-recipient-field = "Remote-Recipient" ":" xtext

remote-status-field = "Remote-Status" ":" xtext

action-value = "failed" / "delayed" / "delivered" / "relayed"

status-code = 3*DIGIT

mts-type = atom

; NOTE: For fields whose field-body is defined as 'xtext',
; the normal RFC 822 special characters are not used.
; text enclosed in paraenthesis is treated as a comment,
; but such comments are not considered separators for
; the purpose of lexical analysis.  Except for comments
; and escaped-crlf's, all characters are significant.
; RFC 1522 encoded-words may NOT be used in xtext.

xtext = *( xchar / hexchar / escaped-crlf )

xchar = any ASCII CHAR between SPACE (32) and TILDE (126)
inclusive, except for "#", "\" and "(".

; "hexchar"s are used to encode octets that cannot be represented
; as plain text, either because they are reserved, or because
; they are non-printable.

hexchar = ASCII "#" immediately followed by two upper
case hexadecimal digits

; An escaped-crlf may appear at the end of a line to allow the
; field to be continued to the next line without inserting any
; white space.



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escaped-crlf = "\" immediately followed by the characters: CR LF SPACE




















































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13. Appendix - 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.


13.1 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.  The
information may be transmitted in the mts-specific fields of a DSN that
are defined in this memo, or if necessary, in extension fields.

The gateway MUST attempt to supply reasonable values for the per-
recipient 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 status from the foreign system.  In this case, the gateway
should make a best effort, falling back on "generic" codes such as 200
(success), 400 (temporary failure), and 500 (permanent failure) when
necessary.

The sender-specified recipient address, if available, should be
preserved in the original-recipient field.

The gateway should also attempt to preserve the "final" recipient
addresses, mta names, and status codes from the foreign system.  Because
DSN fields are limited to the ASCII character set, it may be necessary
to encode foreign protocol elements as printable ASCII values.  The
encoding method is specific to the MTS-type from which the delivery
report is being received.  "remote" values, when available, should be
similarly preserved.

If it is desirable to provide transparent tunneling of the foreign
delivery status notifications through Internet mail, the gateway
specification may define per-recipient extension fields to carry
additional mts-specific information as necessary.


13.2 using xtext.





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     9.2 Gatewaying from DSNs to other mail systems

     A DSN may be gatewayed from the Internet to 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, and
     the latest
available delivery status code.  Each of these must be in the original
sender's format.

If the original-recipient address is available, (success, failure, or temporary failure), and
     for failed deliveries, a diagnostic code that describes the original-mts-
type matches the destination MTS, the original-recipient address should
be provided in the resulting foreign delivery status report.  Otherwise,
the gateway may translate the "canonical" recipient address into the
convention required by reason
     for the destination system.  The final- or remote-
recipient addresses may also be used.  However, due to address
translation and mail forwarding, failure.  Ideally, each of these may have little or no resemblance
to will be in the original recipient address.

If
     sender's format.

     The gateway should make an attempt to preserve the remote-status code is available Original-
     Recipient address and Original-Envelope-ID (if present), in the remote-mts-type matches
     resulting foreign delivery status report.

     When reporting delivery failures, if the MTS to which diagnostic-type subfield
     of the DSN is being gatewayed, Diagnostic-Code field indicates that the remote-status original diagnostic
     code can
be used directly.  Otherwise, if the final-mts-type matches is understood by the destination MTS, environment, the final-status code may information
     from the Diagnostic-Code field should be used.  Failing that, the
"canonical" status-code may
     information in the Status field should be mapped into the set of status codes closest
     available diagnostic code used
by in the destination MTS. environment.

     If it is possible to tunnel a DSN through the destination MTS,
     environment, the gateway specification may define a means of
     preserving the DSN information in the delivery status reports used
     by the destination MTS.
Such encapsulation will necessarily be specific to that particular MTS. environment.




















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14. January 1995



     10. Appendix - Guidelines for use of DSNs by mailing list expanders

     DSNs are designed to be used by mailing list expanders 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
     expander 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 nondelivery reports.  A "smart" mailing list expander can
     therefore intercept such nondelivery 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 Original-Recipient field should be used if available, since it
     should exactly match the subscriber address known to the list.  If
     the
original-recipient 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 one of the 'status'
codes Status and the 'action' field.  Recipients
     Action fields.  Reports for recipients with action values other
     than
"failed" "failure" can generally be ignored; in particular, subscribers
     should not be removed from a list due to "delayed" DSNs.  The latest possible
status code understood by the list expander should be used; the 'remote-
status' code is best, followed by the 'final-status' code (if the codes
for the final or remote MTS-type are understood by the list expander),
and finally the 'status' code. 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 expander not delete a subscriber based on any single failed
     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.  When choosing
whether to delete a subscriber,  Once
     more precise status codes are defined, it may be useful to
     differentiate between the status codes. 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 which persists persisted for several days can usually could be
     considered a reliable that indication that address is were no longer valid.







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15.



     11. Appendix - Examples

     NOTE:  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 MTS-type *-type subfield names or extension fields in
     these examples is not to be construed as a definition for those MTS-types
     type names or extension fields.

     These examples were manually translated from bounced messages using
     whatever information was available.









































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15.1 January 1995



     11.1  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

Original-MTS-Type: INTERNET
Final-MTS-Type: INTERNET

     Final-MTA: dns; cs.utk.edu

Recipient:

     Original-Recipient: rfc822; louisl@larry.slip.umd.edu
     Final-Recipient: rfc822; louisl@larry.slip.umd.edu
     Action: failed failure
     Status: 4.0.0
     Diagnostic-Code: smtp; 426 (connection timed out)
Date:
     Last-Attempt-Date: Thu, 7 Jul 1994 17:15:49 -0400
Original-Recipient: louisl@larry.slip.umd.edu

     --RAA14128.773615765/CS.UTK.EDU
     content-type: message/rfc822

     [original message goes here]
     --RAA14128.773615765/CS.UTK.EDU--









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15.2 January 1995



     11.2  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

Original-MTS-Type: INTERNET

     Final-MTA: dns; cs.utk.edu
Final-MTS-Type: INTERNET

Recipient:

     Original-Recipient: rfc822 ; arathib@vnet.ibm.com
     Final-Recipient: rfc822 ; arathib@vnet.ibm.com
     Action: failed failure
     Status: 5.0.0 (permanent failure)
     Diagnostic-Code: smtp; 550
      ('arathib@vnet.IBM.COM' is not a registered gateway user)
Remote-MTS-Type: INTERNET
     Remote-MTA: dns; vnet.ibm.com

     Original-Recipient: arathib@vnet.ibm.com

Recipient: rfc822; johnh@hpnjld.njd.hp.com
     Final-Recipient: rfc822; johnh@hpnjld.njd.hp.com
     Action: delayed
     Status: 466 4.0.0 (hpnjld.njd.jp.com: host name lookup failure)

     Original-Recipient: johnh@hpnjld.njd.hp.com

Recipient: rfc822; wsnell@sdcc13.ucsd.edu
     Final-Recipient: rfc822; wsnell@sdcc13.ucsd.edu
     Action: failed failure
     Status: 5.0.0
     Diagnostic-Code: smtp; 550 (user unknown)
Remote-MTS-Type: INTERNET
     Remote-MTA: dns; sdcc13.ucsd.edu
Original-Recipient: wsnell@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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15.3



     11.3 A delivery report generated by Message Router (MAILBUS) and
     gatewayed by PMDF_MR to a DSN.  I assume that PMDF_MR could have
preserved the MAILBUS status code in  In this case the DSN (NOTE IN DRAFT: right
Ned?), I just don't know what it would be. 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

     Final-MTA: mailbus; SYS30
Final-MTS-Type: mailbus

Recipient: nair_s@SYS30.timeplex.com

     Final-Recipient: unknown; nair_s
     Status: 500 5.0.0 (unknown permanent failure)
     Action: failed
Final-Recipient: nair_s
Final-Status: ??? (no matching directory entry found) failure
     --[;84229080704991/122306@SYS30]--























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15.4 January 1995



     11.4 A delay report from a multiprotocol MTA.  Note that there is
     no returned content; content, so no third body part appears in the DSN.


     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>;
     Sun, 10 Jul 1994 00:36:51 +0100
     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

Final-MTS-Type: INTERNET
Final-MTA: sun2.nsfnet-relay.ac.uk

Recipient: thomas@de-montfort.ac.uk
Status: 400 (unknown temporary failure)
Action: delayed
--foobar--




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15.5  A DSN gatewayed from a X.400 nondelivery notification


From: "UK.AC.NSF MTA" <postmaster@nsfnet-relay.ac.uk>
To: na-digest-bounces@netlib2.cs.utk.edu
Subject: Delivery Report (failure) for sdz009@prime.napier.ac.uk
Date: Mon, 11 Jul 1994 02:09:43 +0100
Message-ID: <"sun3.nsfne.309:11.06.94.01.09.27"@nsfnet-relay.ac.uk>
content-type: multipart/report; report-type=delivery-status;
      boundary=foobar

--foobar
content-type: text/plain

This report relates to your message: Subject: NA Digest, V. 94, # 27,
  Message-ID: <199407031824.OAA23971@localhost>,
  To: na-digest list:;
        of Sun, 3 Jul 1994 19:47:56 +0100

Your message was not delivered to   sdz009@prime.napier.ac.uk
        for the following reason:
        Message timed out

--foobar
content-type: message/delivery-status

Final-MTS-Type: X400
Final-MTA:  sun3.nsfnet-relay.ac.uk in /PRMD=uk.ac/ADMD= /C=gb/

Recipient: sdz009@prime.napier.ac.uk
Action: failed
Status: 400 (unknown temporary failure)
Final-Recipient: /S=sdz009/OU=prime/O=napier/PRMD=UK.AC/ADMD= /C=GB/
Final-Status: 1/5 (unable-to-transfer/maximum-time-expired)
X400-Subject-Intermediate-Trace-Information: /PRMD=uk.ac/ADMD= /C=gb/
      arrival Sun, 3 Jul 1994 19:47:56 +0100 action Relayed
X400-Subject-Intermediate-Trace-Information: /PRMD=uk.ac/ADMD= /C=gb/
      arrival Sun, 3 Jul 1994 19:24:03 +0100 action Relayed multipart/report; report-type=delivery-status;
           boundary=foobar

     --foobar
     content-type: message/rfc822

[returned content]
--foobar--










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16. Appendix - changes since the July 14 draft

 1. Title and order of paragraphs in section 3 changed text/plain

     The following message:

     UA-ID:  Reliable PC (...
     Q-ID:   sun2.nsf:77/msg.11820-0

     has not been delivered to describe the
    overall structure of the message before intended recipient:

     thomas@de-montfort.ac.uk

     despite repeated delivery attempts over the description past 24 hours.

     The  usual cause of the
    message/delivery-status content-type.

 2. Some text added to section 3 to explicitly state that comments and
    continuation lines are allowed in the same manner as in RFC 822.

 3. Some fields are now explicitly marked as case-sensitive or
    case-insensitive.

 4. "Rcpt" this problem is now spelled "Recipient" in notification fields, and that the
    "INET" MTS-Type remote system is now "INTERNET".

 5. "X-" MTS-types are now allowed.

 6. Received-From field added.

 7. Section 3.2.1.2: added example to show how action and status-codes
    work, contrasting conversion-with-loss with conversion-prohibited.

 8. Changed 'xchar' grammar
     temporarily unavailable.

     Delivery will continue to disallow the characters "(", "#", and
    "\"; added "#"XX notation for hexadecimal encoding; added "\" CR LF
    SPACE notation be attempted up to allow transparent continuation a total elapsed
     time of lines.

 9. Section 3.2.1.3: clarified "MUST be present for each recipient" ->
    "MUST  168 hours, ie 7 days.

     You  will  be present for each delivery attempt...".

10. Section 3.2.2.6: deleted the text which said that the
    final-recipient field shouldn't appear  informed  if it is redundant with either
    original-recipient or recipient.

11. Section 3.2.2.11: fixed incomplete sentence.

12. Section 5: added note about the use of DSNs by mailing lists.

13. Appendix 10: removed description of x1z status-codes; these are
    useful in SMTP (e.g. HELP command) but are not applicable to  delivery
    status reports.

15. Added text to clarify the difference between original, final, and
    remote MTAs.

15. Add text proves to suggest that subject, date, and message-id be retained
    in impossible
     within this time.

     Please quote the third (returned content) body part of a DSN.

16. Added some prose to (sort-of) define "MTS".

17. Added Arrival-date per-message field. Q-ID in any queries regarding this mail.

     --foobar
     content-type: message/delivery-status

     Final-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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18. Added Expiry-date per-recipient field.

19. Added more prose to say that (a) a single January 1995



     11.5  A DSN can describe
    delivery status for multiple recipients of the same message, but (b)
    the delivery status for all recipients of the same message doesn't
    have to be in a single DSN, and (c) gatewayed from a single DSN cannot describe
    delivery events X.400 nondelivery notification


     From: "UK.AC.NSF MTA" <postmaster@nsfnet-relay.ac.uk>
     To: na-digest-bounces@netlib2.cs.utk.edu
     Subject: Delivery Report (failure) for multiple messages.

20.  Expanded the security considerations section.

21.  Explicitly allow the first body part of a DSN to be a
    multipart/alternative.

22.  Add a note to the effect that comments may be used in the
    status-code field.

23.  Added an appendix about use of DSNs by mailing lists.

24.  Renumbered references.

25.  Added prose in the acknowledgements section.  (Please let me know
    if I've left anybody out!  -km)

26.  Explicitly allow encoded-words in comments.

27.  Allow an optional "route" sdz009@prime.napier.ac.uk
     Date: Mon, 11 Jul 1994 02:09:43 +0100
     Message-ID: <"sun3.nsfne.309:11.06.94.01.09.27"@nsfnet-relay.ac.uk>
     content-type: multipart/report; report-type=delivery-status;
           boundary=foobar

     --foobar
     content-type: text/plain

     This report relates to appear in the 'recipient' field,
    and in {final,remote}-recipient fields your message: Subject: NA Digest, V. 94, # 27,
       Message-ID: <199407031824.OAA23971@localhost>,
       To: na-digest list:;
             of the "internet" mts-type.

28.  Fix a few troff glitches.
                                STILL TO DO

 1. Change "original-xxx" Sun, 3 Jul 1994 19:47:56 +0100

     Your message was not delivered to "earliest-xxx" (if I can find   sdz009@prime.napier.ac.uk
             for the
    right words...)

 2. Figure following reason:
             Message timed out and describe how to treat DSNs which result from
    multi-recipient mail forwarding.  Intentions: (a) make the result
    unambiguous and meaningful to the sender, (b) uniform handling -
    don't make handing of "delivered" DSNs too different from
    "relayed/delayed/failed" DSNs.

     --foobar
     content-type: message/delivery-status

     Final-MTA: dns; sun3.nsfnet-relay.ac.uk
      (in /PRMD=uk.ac/ADMD= /C=gb/)

     Original-Recipient: rfc822; sdz009@prime.napier.ac.uk
     Final-Recipient: x400;
      /S=sdz009/OU=prime/O=napier/PRMD=UK.AC/ADMD=+20/C=GB/
     Action: failure
     Status: 4.0.0
     Diagnostic-Code: x400 ; 1/5
      (unable-to-transfer/maximum-time-expired)
     X400-Subject-Intermediate-Trace-Information:
      /PRMD=uk.ac/ADMD= /C=gb/
      arrival Sun, 3 Jul 1994 19:47:56 +0100 action Relayed
     X400-Subject-Intermediate-Trace-Information:
      /PRMD=uk.ac/ADMD= /C=gb/
      arrival Sun, 3 Jul 1994 19:24:03 +0100 action Relayed

     --foobar
     content-type: message/rfc822

     [returned content]
     --foobar--






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