Network Working Group                                           K. Moore
Request for Comments: 1891                       University of Tennessee
Category: Standards Track                                   January 1996


                        SMTP Service Extension
                  for Delivery Status Notifications

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

1. Abstract

  This memo defines an extension to the SMTP service, which allows an
  SMTP client to specify (a) that delivery status notifications (DSNs)
  should be generated under certain conditions, (b) whether such
  notifications should return the contents of the message, and (c)
  additional information, to be returned with a DSN, that allows the
  sender to identify both the recipient(s) for which the DSN was
  issued, and the transaction in which the original message was sent.

  Any questions, comments, and reports of defects or ambiguities in
  this specification may be sent to the mailing list for the NOTARY
  working group of the IETF, using the address
  <[email protected]>.  Requests to subscribe to the mailing
  list should be addressed to <[email protected]>.
  Implementors of this specification are encouraged to subscribe to the
  mailing list, so that they will quickly be informed of any problems
  which might hinder interoperability.

  NOTE: This document is a Proposed Standard.  If and when this
  protocol is submitted for Draft Standard status, any normative text
  (phrases containing SHOULD, SHOULD NOT, MUST, MUST NOT, or MAY) in
  this document will be re-evaluated in light of implementation
  experience, and are thus subject to change.

2. Introduction

  The SMTP protocol [1] requires that an SMTP server provide
  notification of delivery failure, if it determines that a message
  cannot be delivered to one or more recipients.  Traditionally, such
  notification consists of an ordinary Internet mail message (format
  defined by [2]), sent to the envelope sender address (the argument of



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  the SMTP MAIL command), containing an explanation of the error and at
  least the headers of the failed message.

  Experience with large mail distribution lists [3] indicates that such
  messages are often insufficient to diagnose problems, or even to
  determine at which host or for which recipients a problem occurred.
  In addition, the lack of a standardized format for delivery
  notifications in Internet mail makes it difficult to exchange such
  notifications with other message handling systems.

  Such experience has demonstrated a need for a delivery status
  notification service for Internet electronic mail, which:

(a) is reliable, in the sense that any DSN request will either be
   honored at the time of final delivery, or result in a response
   that indicates that the request cannot be honored,

(b) when both success and failure notifications are requested,
   provides an unambiguous and nonconflicting indication of whether
   delivery of a message to a recipient succeeded or failed,

(c) is stable, in that a failed attempt to deliver a DSN should never
   result in the transmission of another DSN over the network,

(d) preserves sufficient information to allow the sender to identify
   both the mail transaction and the recipient address which caused
   the notification, even when mail is forwarded or gatewayed to
   foreign environments, and

(e) interfaces acceptably with non-SMTP and non-822-based mail
   systems, both so that notifications returned from foreign mail
   systems may be useful to Internet users, and so that the
   notification requests from foreign environments may be honored.
   Among the requirements implied by this goal are the ability to
   request non-return-of-content, and the ability to specify whether
   positive delivery notifications, negative delivery notifications,
   both, or neither, should be issued.

  In an attempt to provide such a service, this memo uses the mechanism
  defined in [4] to define an extension to the SMTP protocol.  Using
  this mechanism, an SMTP client may request that an SMTP server issue
  or not issue a delivery status notification (DSN) under certain
  conditions.  The format of a DSN is defined in [5].








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3. Framework for the Delivery Status Notification Extension

  The following service extension is therefore defined:

(1) The name of the SMTP service extension is "Delivery Status
   Notification";

(2) the EHLO keyword value associated with this extension is "DSN",
   the meaning of which is defined in section 4 of this memo;

(3) no parameters are allowed with this EHLO keyword value;

(4) two optional parameters are added to the RCPT command, and two
   optional parameters are added to the MAIL command:

   An optional parameter for the RCPT command, using the
   esmtp-keyword "NOTIFY", (to specify the conditions under which a
   delivery status notification should be generated), is defined in
   section 5.1,

   An optional parameter for the RCPT command, using the
   esmtp-keyword "ORCPT", (used to convey the "original"
   (sender-specified) recipient address), is defined in section 5.2,
   and

   An optional parameter for the MAIL command, using the
   esmtp-keyword "RET", (to request that DSNs containing an
   indication of delivery failure either return the entire contents
   of a message or only the message headers), is defined in section
   5.3,

   An optional parameter for the MAIL command, using the
   esmtp-keyword "ENVID", (used to propagate an identifier for this
   message transmission envelope, which is also known to the sender
   and will, if present, be returned in any DSNs issued for this
   transmission), is defined in section 5.4;

(5) no additional SMTP verbs are defined by this extension.

  The remainder of this memo specifies how support for the extension
  effects the behavior of a message transfer agent.

4.  The Delivery Status Notification service extension

  An SMTP client wishing to request a DSN for a message may issue the
  EHLO command to start an SMTP session, to determine if the server
  supports any of several service extensions.  If the server responds
  with code 250 to the EHLO command, and the response includes the EHLO



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  keyword DSN, then the Delivery Status Notification extension (as
  described in this memo) is supported.

  Ordinarily, when an SMTP server returns a positive (2xx) reply code
  in response to a RCPT command, it agrees to accept responsibility for
  either delivering the message to the named recipient, or sending a
  notification to the sender of the message indicating that delivery
  has failed.  However, an extended SMTP ("ESMTP") server which
  implements this service extension will accept an optional NOTIFY
  parameter with the RCPT command. If present, the NOTIFY parameter
  alters the conditions for generation of delivery status notifications
  from the default (issue notifications only on failure) specified in
  [1].  The ESMTP client may also request (via the RET parameter)
  whether the entire contents of the original message should be
  returned (as opposed to just the headers of that message), along with
  the DSN.

  In general, an ESMTP server which implements this service extension
  will propagate delivery status notification requests when relaying
  mail to other SMTP-based MTAs which also support this extension, and
  make a "best effort" to ensure that such requests are honored when
  messages are passed into other environments.

  In order that any delivery status notifications thus generated will
  be meaningful to the sender, any ESMTP server which supports this
  extension will attempt to propagate the following information to any
  other MTAs that are used to relay the message, for use in generating
  DSNs:

(a) for each recipient, a copy of the original recipient address, as
   used by the sender of the message.

   This address need not be the same as the mailbox specified in the
   RCPT command.  For example, if a message was originally addressed
   to [email protected] and later forwarded to [email protected], after such forwarding has
   taken place, the RCPT command will specify a mailbox of [email protected].
   However, the original recipient address remains [email protected].

   Also, if the message originated from an environment which does not
   use Internet-style user@domain addresses, and was gatewayed into
   SMTP, the original recipient address will preserve the original
   form of the recipient address.

(b) for the entire SMTP transaction, an envelope identification
   string, which may be used by the sender to associate any delivery
   status notifications with the transaction used to send the
   original message.




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5.  Additional parameters for RCPT and MAIL commands

  The extended RCPT and MAIL commands are issued by a client when it
  wishes to request a DSN from the server, under certain conditions,
  for a particular recipient.  The extended RCPT and MAIL commands are
  identical to the RCPT and MAIL commands defined in [1], except that
  one or more of the following parameters appear after the sender or
  recipient address, respectively.  The general syntax for extended
  SMTP commands is defined in [4].

  NOTE: Although RFC 822 ABNF is used to describe the syntax of these
  parameters, they are not, in the language of that document,
  "structured field bodies".  Therefore, while parentheses MAY appear
  within an emstp-value, they are not recognized as comment delimiters.

  The syntax for "esmtp-value" in [4] does not allow SP, "=", control
  characters, or characters outside the traditional ASCII range of 1-
  127 decimal to be transmitted in an esmtp-value.  Because the ENVID
  and ORCPT parameters may need to convey values outside this range,
  the esmtp-values for these parameters are encoded as "xtext".
  "xtext" is formally defined as follows:

    xtext = *( xchar / hexchar )

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

; "hexchar"s are intended to encode octets that cannot appear
; as ASCII characters within an esmtp-value.

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

When encoding an octet sequence as xtext:

+ Any ASCII CHAR between "!" and "~" inclusive, except for "+" and "=",
 MAY be encoded as itself.  (A CHAR in this range MAY instead be
 encoded as a "hexchar", at the implementor's discretion.)

+ ASCII CHARs that fall outside the range above must be encoded as
 "hexchar".

5.1  The NOTIFY parameter of the ESMTP RCPT command

  A RCPT command issued by a client may contain the optional esmtp-
  keyword "NOTIFY", to specify the conditions under which the SMTP
  server should generate DSNs for that recipient.  If the NOTIFY
  esmtp-keyword is used, it MUST have an associated esmtp-value,



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  formatted according to the following rules, using the ABNF of RFC
  822:

    notify-esmtp-value = "NEVER" / 1#notify-list-element

    notify-list-element = "SUCCESS" / "FAILURE" / "DELAY"

Notes:

a. Multiple notify-list-elements, separated by commas, MAY appear in a
  NOTIFY parameter; however, the NEVER keyword MUST appear by itself.

b. Any of the keywords NEVER, SUCCESS, FAILURE, or DELAY may be spelled
  in any combination of upper and lower case letters.

The meaning of the NOTIFY parameter values is generally as follows:

+ A NOTIFY parameter value of "NEVER" requests that a DSN not be
 returned to the sender under any conditions.

+ A NOTIFY parameter value containing the "SUCCESS" or "FAILURE"
 keywords requests that a DSN be issued on successful delivery or
 delivery failure, respectively.

+ A NOTIFY parameter value containing the keyword "DELAY" indicates the
 sender's willingness to receive "delayed" DSNs.  Delayed DSNs may be
 issued if delivery of a message has been delayed for an unusual amount
 of time (as determined by the MTA at which the message is delayed),
 but the final delivery status (whether successful or failure) cannot
 be determined.  The absence of the DELAY keyword in a NOTIFY parameter
 requests that a "delayed" DSN NOT be issued under any conditions.

  The actual rules governing interpretation of the NOTIFY parameter are
  given in section 6.

  For compatibility with SMTP clients that do not use the NOTIFY
  facility, the absence of a NOTIFY parameter in a RCPT command may be
  interpreted as either NOTIFY=FAILURE or NOTIFY=FAILURE,DELAY.

5.2 The ORCPT parameter to the ESMTP RCPT command

  The ORCPT esmtp-keyword of the RCPT command is used to specify an
  "original" recipient address that corresponds to the actual recipient
  to which the message is to be delivered.  If the ORCPT esmtp-keyword
  is used, it MUST have an associated esmtp-value, which consists of
  the original recipient address, encoded according to the rules below.
  The ABNF for the ORCPT parameter is:




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    orcpt-parameter = "ORCPT=" original-recipient-address

    original-recipient-address = addr-type ";" xtext

    addr-type = atom

  The "addr-type" portion MUST be an IANA-registered electronic mail
  address-type (as defined in [5]), while the "xtext" portion contains
  an encoded representation of the original recipient address using the
  rules in section 5 of this document.  The entire ORCPT parameter MAY
  be up to 500 characters in length.

  When initially submitting a message via SMTP, if the ORCPT parameter
  is used, it MUST contain the same address as the RCPT TO address
  (unlike the RCPT TO address, the ORCPT parameter will be encoded as
  xtext).  Likewise, when a mailing list submits a message via SMTP to
  be distributed to the list subscribers, if ORCPT is used, the ORCPT
  parameter MUST match the new RCPT TO address of each recipient, not
  the address specified by the original sender of the message.)

  The "addr-type" portion of the original-recipient-address is used to
  indicate the "type" of the address which appears in the ORCPT
  parameter value.  However, the address associated with the ORCPT
  keyword is NOT constrained to conform to the syntax rules for that
  "addr-type".

  Ideally, the "xtext" portion of the original-recipient-address should
  contain, in encoded form, the same sequence of characters that the
  sender used to specify the recipient.  However, for a message
  gatewayed from an environment (such as X.400) in which a recipient
  address is not a simple string of printable characters, the
  representation of recipient address must be defined by a
  specification for gatewaying between DSNs and that environment.

5.3 The RET parameter of the ESMTP MAIL command

  The RET esmtp-keyword on the extended MAIL command specifies whether
  or not the message should be included in any failed DSN issued for
  this message transmission.  If the RET esmtp-keyword is used, it MUST
  have an associated esmtp-value, which is one of the following
  keywords:

  FULL  requests that the entire message be returned in any "failed"
        delivery status notification issued for this recipient.

  HDRS  requests that only the headers of the message be returned.





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  The FULL and HDRS keywords may be spelled in any combination of upper
  and lower case letters.

  If no RET parameter is supplied, the MTA MAY return either the
  headers of the message or the entire message for any DSN containing
  indication of failed deliveries.

  Note that the RET parameter only applies to DSNs that indicate
  delivery failure for at least one recipient.  If a DSN contains no
  indications of delivery failure, only the headers of the message
  should be returned.

5.4  The ENVID parameter to the ESMTP MAIL command

  The ENVID esmtp-keyword of the SMTP MAIL command is used to specify
  an "envelope identifier" to be transmitted along with the message and
  included in any DSNs issued for any of the recipients named in this
  SMTP transaction.  The purpose of the envelope identifier is to allow
  the sender of a message to identify the transaction for which the DSN
  was issued.

  The ABNF for the ENVID parameter is:

    envid-parameter = "ENVID=" xtext

  The ENVID esmtp-keyword MUST have an associated esmtp-value.  No
  meaning is assigned by the mail system to the presence or absence of
  this parameter or to any esmtp-value associated with this parameter;
  the information is used only by the sender or his user agent.  The
  ENVID parameter MAY be up to 100 characters in length.

5.5 Restrictions on the use of Delivery Status Notification parameters

  The RET and ENVID parameters MUST NOT appear more than once each in
  any single MAIL command.  If more than one of either of these
  parameters appears in a MAIL command, the ESMTP server SHOULD respond
  with "501 syntax error in parameters or arguments".

  The NOTIFY and ORCPT parameters MUST NOT appear more than once in any
  RCPT command.  If more than one of either of these parameters appears
  in a RCPT command, the ESMTP server SHOULD respond with "501 syntax
  error in parameters or arguments".

6. Conformance requirements

  The Simple Mail Transfer Protocol (SMTP) is used by Message Transfer
  Agents (MTAs) when accepting, relaying, or gatewaying mail, as well
  as User Agents (UAs) when submitting mail to the mail transport



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  system.  The DSN extension to SMTP may be used to allow UAs to convey
  the sender's requests as to when DSNs should be issued.  A UA which
  claims to conform to this specification must meet certain
  requirements as described below.

  Typically, a message transfer agent (MTA) which supports SMTP will
  assume, at different times, both the role of a SMTP client and an
  SMTP server, and may also provide local delivery, gatewaying to
  foreign environments, forwarding, and mailing list expansion.  An MTA
  which, when acting as an SMTP server, issues the DSN keyword in
  response to the EHLO command, MUST obey the rules below for a
  "conforming SMTP client" when acting as a client, and a "conforming
  SMTP server" when acting as a server.  The term "conforming MTA"
  refers to an MTA which conforms to this specification, independent of
  its role of client or server.

6.1 SMTP protocol interactions

  The following rules apply to SMTP transactions in which any of the
  ENVID, NOTIFY, RET, or ORCPT keywords are used:

(a) If an SMTP client issues a MAIL command containing a valid ENVID
   parameter and associated esmtp-value and/or a valid RET parameter
   and associated esmtp-value, a conforming SMTP server MUST return
   the same reply-code as it would to the same MAIL command without
   the ENVID and/or RET parameters.  A conforming SMTP server MUST
   NOT refuse a MAIL command based on the absence or presence of
   valid ENVID or RET parameters, or on their associated
   esmtp-values.

   However, if the associated esmtp-value is not valid (i.e. contains
   illegal characters), or if there is more than one ENVID or RET
   parameter in a particular MAIL command, the server MUST issue the
   reply-code 501 with an appropriate message (e.g.  "syntax error in
   parameter").

(b) If an SMTP client issues a RCPT command containing any valid
   NOTIFY and/or ORCPT parameters, a conforming SMTP server MUST
   return the same response as it would to the same RCPT command
   without those NOTIFY and/or ORCPT parameters.  A conforming SMTP
   server MUST NOT refuse a RCPT command based on the presence or
   absence of any of these parameters.

   However, if any of the associated esmtp-values are not valid, or
   if there is more than one of any of these parameters in a
   particular RCPT command, the server SHOULD issue the response "501
   syntax error in parameter".




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6.2 Handling of messages received via SMTP

  This section describes how a conforming MTA should handle any
  messages received via SMTP.

  NOTE: A DSN MUST NOT be returned to the sender for any message for
  which the return address from the SMTP MAIL command was NULL ("<>"),
  even if the sender's address is available from other sources (e.g.
  the message header).  However, the MTA which would otherwise issue a
  DSN SHOULD inform the local postmaster of delivery failures through
  some appropriate mechanism that will not itself result in the
  generation of DSNs.

  DISCUSSION: RFC 1123, section 2.3.3 requires error notifications to
  be sent with a NULL return address ("reverse-path").  This creates an
  interesting situation when a message arrives with one or more
  nonfunctional recipient addresses in addition to a nonfunctional
  return address.  When delivery to one of the recipient addresses
  fails, the MTA will attempt to send a nondelivery notification to the
  return address, setting the return address on the notification to
  NULL.  When the delivery of this notification fails, the MTA
  attempting delivery of that notification sees a NULL return address.
  If that MTA were not to inform anyone of the situation, the original
  message would be silently lost.  Furthermore, a nonfunctional return
  address is often indicative of a configuration problem in the
  sender's MTA.  Reporting the condition to the local postmaster may
  help to speed correction of such errors.

6.2.1 Relay of messages to other conforming SMTP servers

  The following rules govern the behavior of a conforming MTA, when
  relaying a message which was received via the SMTP protocol, to an
  SMTP server that supports the Delivery Status Notification service
  extension:

(a) Any ENVID parameter included in the MAIL command when a message was
   received, MUST also appear on the MAIL command with which the
   message is relayed, with the same associated esmtp-value.  If no
   ENVID parameter was included in the MAIL command when the message
   was received, the ENVID parameter MUST NOT be supplied when the
   message is relayed.

(b) Any RET parameter included in the MAIL command when a message was
   received, MUST also appear on the MAIL command with which the
   message is relayed, with the same associated esmtp-value.  If no RET
   parameter was included in the MAIL command when the message was
   received, the RET parameter MUST NOT supplied when the message is
   relayed.



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(c) If the NOTIFY parameter was supplied for a recipient when the
   message was received, the RCPT command issued when the message is
   relayed MUST also contain the NOTIFY parameter along with its
   associated esmtp-value.  If the NOTIFY parameter was not supplied
   for a recipient when the message was received, the NOTIFY parameter
   MUST NOT be supplied for that recipient when the message is relayed.

(d) If any ORCPT parameter was present in the RCPT command for a
   recipient when the message was received, an ORCPT parameter with the
   identical original-recipient-address MUST appear in the RCPT command
   issued for that recipient when relaying the message.  (For example,
   the MTA therefore MUST NOT change the case of any alphabetic
   characters in an ORCPT parameter.)

   If no ORCPT parameter was present in the RCPT command when the
   message was received, an ORCPT parameter MAY be added to the RCPT
   command when the message is relayed.  If an ORCPT parameter is added
   by the relaying MTA, it MUST contain the recipient address from the
   RCPT command used when the message was received by that MTA.

6.2.2  Relay of messages to non-conforming SMTP servers

  The following rules govern the behavior of a conforming MTA (in the
  role of client), when relaying a message which was received via the
  SMTP protocol, to an SMTP server that does not support the Delivery
  Status Notification service extension:

(a) ENVID, NOTIFY, RET, or ORCPT parameters MUST NOT be issued when
   relaying the message.

(b) If the NOTIFY parameter was supplied for a recipient, with an esmtp-
   value containing the keyword SUCCESS, and the SMTP server returns a
   success (2xx) reply-code in response to the RCPT command, the client
   MUST issue a "relayed" DSN for that recipient.

(c) If the NOTIFY parameter was supplied for a recipient with an esmtp-
   value containing the keyword FAILURE, and the SMTP server returns a
   permanent failure (5xx) reply-code in response to the RCPT command,
   the client MUST issue a "failed" DSN for that recipient.

(d) If the NOTIFY parameter was supplied for a recipient with an esmtp-
   value of NEVER, the client MUST NOT issue a DSN for that recipient,
   regardless of the reply-code returned by the SMTP server.  However,
   if the server returned a failure (5xx) reply-code, the client MAY
   inform the local postmaster of the delivery failure via an
   appropriate mechanism that will not itself result in the generation
   of DSNs.




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   When attempting to relay a message to an SMTP server that does not
   support this extension, and if NOTIFY=NEVER was specified for some
   recipients of that message, a conforming SMTP client MAY relay the
   message for those recipients in a separate SMTP transaction, using
   an empty reverse-path in the MAIL command.  This will prevent DSNs
   from being issued for those recipients by MTAs that conform to [1].

(e) If a NOTIFY parameter was not supplied for a recipient, and the SMTP
   server returns a success (2xx) reply-code in response to a RCPT
   command, the client MUST NOT issue any DSN for that recipient.

(f) If a NOTIFY parameter was not supplied for a recipient, and the SMTP
   server returns a permanent failure (5xx) reply-code in response to a
   RCPT command, the client MUST issue a "failed" DSN for that
   recipient.

6.2.3  Local delivery of messages

  The following rules govern the behavior of a conforming MTA upon
  successful delivery of a message that was received via the SMTP
  protocol, to a local recipient's mailbox:

  "Delivery" means that the message has been placed in the recipient's
  mailbox.  For messages which are transmitted to a mailbox for later
  retrieval via IMAP [6], POP [7] or a similar message access protocol,
  "delivery" occurs when the message is made available to the IMAP
  (POP, etc.) service, rather than when the message is retrieved by the
  recipient's user agent.

  Similarly, for a recipient address which corresponds to a mailing
  list exploder, "delivery" occurs when the message is made available
  to that list exploder, even though the list exploder might refuse to
  deliver that message to the list recipients.

(a) If the NOTIFY parameter was supplied for that recipient, with an
   esmtp-value containing the SUCCESS keyword, the MTA MUST issue a
   "delivered" DSN for that recipient.

(b) If the NOTIFY parameter was supplied for that recipient which did
   not contain the SUCCESS keyword, the MTA MUST NOT issue a DSN for
   that recipient.

(c) If the NOTIFY parameter was not supplied for that recipient, the MTA
   MUST NOT issue a DSN.







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6.2.4  Gatewaying a message into a foreign environment

  The following rules govern the behavior of a conforming MTA, when
  gatewaying a message that was received via the SMTP protocol, into a
  foreign (non-SMTP) environment:

(a) If the the foreign environment is capable of issuing appropriate
   notifications under the conditions requested by the NOTIFY
   parameter, and the conforming MTA can ensure that any notification
   thus issued will be translated into a DSN and delivered to the
   original sender, then the MTA SHOULD gateway the message into the
   foreign environment, requesting notification under the desired
   conditions, without itself issuing a DSN.

(b) If a NOTIFY parameter was supplied with the SUCCESS keyword, but the
   destination environment cannot return an appropriate notification on
   successful delivery, the MTA SHOULD issue a "relayed" DSN for that
   recipient.

(c) If a NOTIFY parameter was supplied with an esmtp-keyword of NEVER, a
   DSN MUST NOT be issued.  If possible, the MTA SHOULD direct the
   destination environment to not issue delivery notifications for that
   recipient.

(d) If the NOTIFY parameter was not supplied for a particular recipient,
   a DSN SHOULD NOT be issued by the gateway. The gateway SHOULD
   attempt to ensure that appropriate notification will be provided by
   the foreign mail environment if eventual delivery failure occurs,
   and that no notification will be issued on successful delivery.

(e) When gatewaying a message into a foreign environment, the return-of-
   content conditions specified by any RET parameter are nonbinding;
   however, the MTA SHOULD attempt to honor the request using whatever
   mechanisms exist in the foreign environment.

6.2.5  Delays in delivery

  If a conforming MTA receives a message via the SMTP protocol, and is
  unable to deliver or relay the message to one or more recipients for
  an extended length of time (to be determined by the MTA), it MAY
  issue a "delayed" DSN for those recipients, subject to the following
  conditions:

(a) If the NOTIFY parameter was supplied for a recipient and its value
   included the DELAY keyword, a "delayed" DSN MAY be issued.

(b) If the NOTIFY parameter was not supplied for a recipient, a
   "delayed" DSN MAY be issued.



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(c) If the NOTIFY parameter was supplied which did not contain the DELAY
   keyword, a "delayed" DSN MUST NOT be issued.

  NOTE: Although delay notifications are common in present-day
  electronic mail, a conforming MTA is never required to issue
  "delayed" DSNs.  The DELAY keyword of the NOTIFY parameter is
  provided to allow the SMTP client to specifically request (by
  omitting the DELAY parameter) that "delayed" DSNs NOT be issued.

6.2.6  Failure of a conforming MTA to deliver a message

  The following rules govern the behavior of a conforming MTA which
  received a message via the SMTP protocol, and is unable to deliver a
  message to a recipient specified in the SMTP transaction:

(a) If a NOTIFY parameter was supplied for the recipient with an esmtp-
   keyword containing the value FAILURE, a "failed" DSN MUST be issued
   by the MTA.

(b) If a NOTIFY parameter was supplied for the recipient which did not
   contain the value FAILURE, a DSN MUST NOT be issued for that
   recipient.  However, the MTA MAY inform the local postmaster of the
   delivery failure via some appropriate mechanism which does not
   itself result in the generation of DSNs.

(c) If no NOTIFY parameter was supplied for the recipient, a "failed"
   DSN MUST be issued.

  NOTE: Some MTAs are known to forward undeliverable messages to the
  local postmaster or "dead letter" mailbox.  This is still considered
  delivery failure, and does not diminish the requirement to issue a
  "failed" DSN under the conditions defined elsewhere in this memo.  If
  a DSN is issued for such a recipient, the Action value MUST be
  "failed".

6.2.7 Forwarding, aliases, and mailing lists

  Delivery of a message to a local email address usually causes the
  message to be stored in the recipient's mailbox.  However, MTAs
  commonly provide a facility where a local email address can be
  designated as an "alias" or "mailing list"; delivery to that address
  then causes the message to be forwarded to each of the (local or
  remote) recipient addresses associated with the alias or list.  It is
  also common to allow a user to optionally "forward" her mail to one
  or more alternate addresses.  If this feature is enabled, her mail is
  redistributed to those addresses instead of being deposited in her
  mailbox.




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  Following the example of [9] (section 5.3.6), this document defines
  the difference between an "alias" and "mailing list" as follows: When
  forwarding a message to the addresses associated with an "alias", the
  envelope return address (e.g. SMTP MAIL FROM) remains intact.
  However, when forwarding a message to the addresses associated with a
  "mailing list", the envelope return address is changed to that of the
  administrator of the mailing list.  This causes DSNs and other
  nondelivery reports resulting from delivery to the list members to be
  sent to the list administrator rather than the sender of the original
  message.

  The DSN processing for aliases and mailing lists is as follows:

6.2.7.1 mailing lists

  When a message is delivered to a list submission address (i.e. placed
  in the list's mailbox for incoming mail, or accepted by the process
  that redistributes the message to the list subscribers), this is
  considered final delivery for the original message.  If the NOTIFY
  parameter for the list submission address contained the SUCCESS
  keyword, a "delivered" DSN MUST be returned to the sender of the
  original message.

  NOTE: Some mailing lists are able to reject message submissions,
  based on the content of the message, the sender's address, or some
  other criteria.  While the interface between such a mailing list and
  its MTA is not well-defined, it is important that DSNs NOT be issued
  by both the MTA (to report successful delivery to the list), and the
  list (to report message rejection using a "failure" DSN.)

  However, even if a "delivered" DSN was issued by the MTA, a mailing
  list which rejects a message submission MAY notify the sender that
  the message was rejected using an ordinary message instead of a DSN.

  Whenever a message is redistributed to an mailing list,

(a) The envelope return address is rewritten to point to the list
   maintainer.  This address MAY be that of a process that recognizes
   DSNs and processes them automatically, but it MUST forward
   unrecognized messages to the human responsible for the list.

(b) The ENVID, NOTIFY, RET, and ORCPT parameters which accompany the
   redistributed message MUST NOT be derived from those of the original
   message.

(c) The NOTIFY and RET parameters MAY be specified by the local
   postmaster or the list administrator.  If ORCPT parameters are
   supplied during redistribution to the list subscribers, they SHOULD



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   contain the addresses of the list subscribers in the format used by
   the mailing list.

6.2.7.2 single-recipient aliases

  Under normal circumstances, when a message arrives for an "alias"
  which has a single forwarding address, a DSN SHOULD NOT be issued.
  Any ENVID, NOTIFY, RET, or ORCPT parameters SHOULD be propagated with
  the message as it is redistributed to the forwarding address.

6.2.7.3 multiple-recipient aliases

  An "alias" with multiple recipient addresses may be handled in any of
  the following ways:

(a) Any ENVID, NOTIFY, RET, or ORCPT parameters are NOT propagated when
   relaying the message to any of the forwarding addresses.  If the
   NOTIFY parameter for the alias contained the SUCCESS keyword, the
   MTA issues a "relayed" DSN.  (In effect, the MTA treats the message
   as if it were being relayed into an environment that does not
   support DSNs.)

(b) Any ENVID, NOTIFY, RET, or ORCPT parameters (or the equivalent
   requests if the message is gatewayed) are propagated to EXACTLY one
   of the forwarding addresses.  No DSN is issued.  (This is
   appropriate when aliasing is used to forward a message to a
   "vacation" auto-responder program in addition to the local mailbox.)

(c) Any ENVID, RET, or ORCPT parameters are propagated to all forwarding
   addresses associated with that alias.  The NOTIFY parameter is
   propagated to the forwarding addresses, except that it any SUCCESS
   keyword is removed.  If the original NOTIFY parameter for the alias
   contained the SUCCESS keyword, an "expanded" DSN is issued for the
   alias.  If the NOTIFY parameter for the alias did not contain the
   SUCCESS keyword, no DSN is issued for the alias.

6.2.7.4 confidential forwarding addresses

  If it is desired to maintain the confidentiality of a recipient's
  forwarding address, the forwarding may be treated as if it were a
  mailing list.  A DSN will be issued, if appropriate, upon "delivery"
  to the recipient address specified by the sender.  When the message
  is forwarded it will have a new envelope return address. Any DSNs
  which result from delivery failure of the forwarded message will not
  be returned to the original sender of the message and thus not expose
  the recipient's forwarding address.





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6.2.8 DSNs describing delivery to multiple recipients

  A single DSN may describe attempts to deliver a message to multiple
  recipients of that message.  If a DSN is issued for some recipients
  in an SMTP transaction and not for others according to the rules
  above, the DSN SHOULD NOT contain information for recipients for whom
  DSNs would not otherwise have been issued.

6.3 Handling of messages from other sources

  For messages which originated from "local" users (whatever that
  means), the specifications under which DSNs should be generated can
  be communicated to the MTA via any protocol agreed on between the
  sender's mail composer (user agent) and the MTA.  The local MTA can
  then either relay the message, or issue appropriate delivery status
  notifications.  However, if such requests are transmitted within the
  message itself (for example in the message headers), the requests
  MUST be removed from the message before it is transmitted via SMTP.

  For messages gatewayed from non-SMTP sources and further relayed by
  SMTP, the gateway SHOULD, using the SMTP extensions described here,
  attempt to provide the delivery reporting conditions expected by the
  source mail environment.  If appropriate, any DSNs returned to the
  source environment SHOULD be translated into the format expected in
  that environment.

6.4  Implementation limits

  A conforming MTA MUST accept ESMTP parameters of at least the
  following sizes:

  (a) ENVID parameter: 100 characters.

  (b) NOTIFY parameter: 28 characters.

  (c) ORCPT parameter: 500 characters.

  (d) RET parameter: 8 characters.

  The maximum sizes for the ENVID and ORCPT parameters are intended to
  be adequate for the transmission of "foreign" envelope identifier and
  original recipient addresses.  However, user agents which use SMTP as
  a message submission protocol SHOULD NOT generate ENVID parameters
  which are longer than 38 characters in length.

  A conforming MTA MUST be able to accept SMTP command-lines which are
  at least 1036 characters long (530 characters for the ORCPT and
  NOTIFY parameters of the RCPT command, in addition to the 512



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  characters required by [1]).  If other SMTP extensions are supported
  by the MTA, the MTA MUST be able to accept a command-line large
  enough for each SMTP command and any combination of ESMTP parameters
  which may be used with that command.

7.  Format of delivery notifications

  The format of delivery status notifications is defined in [5], which
  uses the framework defined in [8].  Delivery status notifications are
  to be returned to the sender of the original message as outlined
  below.

7.1 SMTP Envelope to be used with delivery status notifications

  The DSN sender address (in the SMTP MAIL command) MUST be a null
  reverse-path ("<>"), as required by section 5.3.3 of [9].  The DSN
  recipient address (in the RCPT command) is copied from the MAIL
  command which accompanied the message for which the DSN is being
  issued.  When transmitting a DSN via SMTP, the RET parameter MUST NOT
  be used.  The NOTIFY parameter MAY be used, but its value MUST be
  NEVER.  The ENVID parameter (with a newly generated envelope-id)
  and/or ORCPT parameter MAY be used.

7.2 Contents of the DSN

  A DSN is transmitted as a MIME message with a top-level content-type
  of multipart/report (as defined in [5]).

  The multipart/report content-type may be used for any of several
  kinds of reports generated by the mail system.  When multipart/report
  is used to convey a DSN, the report-type parameter of the
  multipart/report content-type is "delivery-status".

  As described in [8], the first component of a multipart/report
  content-type is a human readable explanation of the report.  For a
  DSN, the second component of the multipart/report is of content-type
  message/delivery-status (defined in [5]).  The third component of the
  multipart/report consists of the original message or some portion
  thereof.  When the value of the RET parameter is FULL, the full
  message SHOULD be returned for any DSN which conveys notification of
  delivery failure.  (However, if the length of the message is greater
  than some implementation-specified length, the MTA MAY return only
  the headers even if the RET parameter specified FULL.)  If a DSN
  contains no notifications of delivery failure, the MTA SHOULD return
  only the headers.

  The third component must have an appropriate content-type label.
  Issues concerning selection of the content-type are discussed in [8].



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7.3 Message/delivery-status fields

  The message/delivery-status content-type defines a number of fields,
  with general specifications for their contents.  The following
  requirements for any DSNs generated in response to a message received
  by the SMTP protocol by a conforming SMTP server, are in addition to
  the requirements defined in [5] for the message/delivery-status type.

  When generating a DSN for a message which was received via the SMTP
  protocol, a conforming MTA will generate the following fields of the
  message/delivery-status body part:

(a) if an ENVID parameter was present on the MAIL command, an Original-
   Envelope-ID field MUST be supplied, and the value associated with
   the ENVID parameter must appear in that field.  If the message was
   received via SMTP with no ENVID parameter, the Original-Envelope-ID
   field MUST NOT be supplied.

   Since the ENVID parameter is encoded as xtext, but the Original-
   Envelope-ID header is NOT encoded as xtext, the MTA must decode the
   xtext encoding when copying the ENVID value to the Original-
   Envelope-ID field.

(b) The Reporting-MTA field MUST be supplied.  If Reporting MTA can
   determine its fully-qualified Internet domain name, the MTA-name-
   type subfield MUST be "dns", and the field MUST contain the fully-
   qualified domain name of the Reporting MTA. If the fully-qualified
   Internet domain name of the Reporting MTA is not known (for example,
   for an SMTP server which is not directly connected to the Internet),
   the Reporting-MTA field may contain any string identifying the MTA,
   however, in this case the MTA-name-type subfield MUST NOT be "dns".
   A MTA-name-type subfield value of "x-local-hostname" is suggested.

(c) Other per-message fields as defined in [5] MAY be supplied as
   appropriate.

(d) If the ORCPT parameter was provided for this recipient, the
   Original-Recipient field MUST be supplied, with its value taken from
   the ORCPT parameter.  If no ORCPT parameter was provided for this
   recipient, the Original-Recipient field MUST NOT appear.

(e) The Final-Recipient field MUST be supplied. It MUST contain the
   recipient address from the message envelope.  If the message was
   received via SMTP, the address-type will be "rfc822".

(f) The Action field MUST be supplied.





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(g) The Status field MUST be supplied, using a status-code from [10].
   If there is no specific code which suitably describes a delivery
   failure, either 4.0.0 (temporary failure), or 5.0.0 (permanent
   failure) MUST be used.

(h) For DSNs resulting from attempts to relay a message to one or more
   recipients via SMTP, the Remote-MTA field MUST be supplied for each
   of those recipients.  The mta-name-type subfields of those Remote-
   MTA fields will be "dns".

(i) For DSNs resulting from attempts to relay a message to one or more
   recipients via SMTP, the Diagnostic-Code MUST be supplied for each
   of those recipients.  The diagnostic-type subfield will be "smtp".
   See section 9.2(a) of this document for a description of the "smtp"
   diagnostic-code.

(j) For DSNs resulting from attempts to relay a message to one or more
   recipients via SMTP, an SMTP-Remote-Recipient extension field MAY be
   supplied for each recipient, which contains the address of that
   recpient which was presented to the remote SMTP server.

(k) Other per-recipient fields defined in [5] MAY appear, as
   appropriate.

8. Acknowledgments

  The author wishes to thank Eric Allman, Harald Alvestrand, Jim
  Conklin, Bryan Costales, Peter Cowen, Dave Crocker, Roger Fajman, Ned
  Freed, Marko Kaittola, Steve Kille, John Klensin, Anastasios
  Kotsikonas, John Gardiner Myers, Julian Onions, Jacob Palme, Marshall
  Rose, Greg Vaudreuil, and Klaus Weide for their suggestions for
  improvement of this document.



















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9. Appendix - Type-Name Definitions

  The following type names are defined for use in DSN fields generated
  by conforming SMTP-based MTAs:

9.1 "rfc822" address-type

  The "rfc822" address-type is to be used when reporting Internet
  electronic mail address in the Original-Recipient and Final-Recipient
  DSN fields.

(a) address-type name: rfc822

(b) syntax for mailbox addresses

   RFC822 mailbox addresses are generally expected to be of the form

   [route] addr-spec

   where "route" and "addr-spec" are defined in [2], and the "domain"
   portions of both "route" and "addr-spec" are fully-qualified domain
   names that are registered in the DNS.  However, an MTA MUST NOT
   modify an address obtained from the message envelope to force it to
   conform to syntax rules.

(c) If addresses of this type are not composed entirely of graphic
characters from the US-ASCII repertoire, a specification for how they
are to be encoded as graphic US-ASCII characters in a DSN Original-
Recipient or Final-Recipient DSN field.

   RFC822 addresses consist entirely of graphic characters from the US-
   ASCII repertoire, so no translation is necessary.

9.2 "smtp" diagnostic-type

  The "smtp" diagnostic-type is to be used when reporting SMTP reply-
  codes in Diagnostic-Code DSN fields.

(a) diagnostic-type name: SMTP

(b) A description of the syntax to be used for expressing diagnostic
codes of this type as graphic characters from the US-ASCII repertoire.

   An SMTP diagnostic-code is of the form

   *( 3*DIGIT "-" *text ) 3*DIGIT SPACE *text





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   For a single-line SMTP reply to an SMTP command, the diagnostic-code
   SHOULD be an exact transcription of the reply.  For multi-line SMTP
   replies, it is necessary to insert a SPACE before each line after
   the first.  For example, an SMTP reply of:

   550-mailbox unavailable
   550 user has moved with no forwarding address

   could appear as follows in a Diagnostic-Code DSN field:

   Diagnostic-Code: smtp ; 550-mailbox unavailable
    550 user has moved with no forwarding address

(c) A list of valid diagnostic codes of this type and the meaning of
each code.

   SMTP reply-codes are currently defined in [1], [4], and [9].
   Additional codes may be defined by other RFCs.

9.3 "dns" MTA-name-type

  The "dns" MTA-name-type should be used in the Reporting-MTA field.
  An MTA-name of type "dns" is a fully-qualified domain name.  The name
  must be registered in the DNS, and the address Postmaster@{mta-name}
  must be valid.

(a) MTA-name-type name: dns

(b) A description of the syntax of MTA names of this type, using BNF,
regular expressions, ASN.1, or other non-ambiguous language.

   MTA names of type "dns" SHOULD be valid Internet domain names.  If
   such domain names are not available, a domain-literal containing the
   internet protocol address is acceptable.  Such domain names
   generally conform to the following syntax:

   domain = real-domain / domain-literal

   real-domain = sub-domain *("." sub-domain)

   sub-domain = atom

   domain-literal = "[" 1*3DIGIT 3("." 1*3DIGIT) "]"

   where "atom" and "DIGIT" are defined in [2].






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(c) If MTA names of this type do not consist entirely of graphic
characters from the US-ASCII repertoire, a specification for how an MTA
name of this type should be expressed as a sequence of graphic US-ASCII
characters.

   MTA names of type "dns" consist entirely of graphic US-ASCII
   characters, so no translation is needed.

10. Appendix - Example

  This example traces the flow of a single message addressed to
  multiple recipients.  The message is sent by [email protected] to
  [email protected], [email protected], [email protected],
  [email protected], [email protected], and [email protected], with a
  variety of per-recipient options.  The message is successfully
  delivered to Bob, Dana (via a gateway), Eric, and Fred.  Delivery
  fails for Carol and George.

  NOTE: Formatting rules for RFCs require that no line be longer than
  72 characters.  Therefore, in the following examples, some SMTP
  commands longer than 72 characters are printed on two lines, with the
  first line ending in "\".  In an actual SMTP transaction, such a
  command would be sent as a single line (i.e. with no embedded CRLFs),
  and without the "\" character that appears in these examples.

10.1 Submission

  Alice's user agent sends the message to the SMTP server at Pure-
  Heart.ORG.  Note that while this example uses SMTP as a mail
  submission protocol, other protocols could also be used.

<<< 220 Pure-Heart.ORG SMTP server here
>>> EHLO Pure-Heart.ORG
<<< 250-Pure-Heart.ORG
<<< 250-DSN
<<< 250-EXPN
<<< 250 SIZE
>>> MAIL FROM:<[email protected]> RET=HDRS ENVID=QQ314159
<<< 250 <[email protected]> sender ok
>>> RCPT TO:<[email protected]> NOTIFY=SUCCESS \
   ORCPT=rfc822;[email protected]
<<< 250 <[email protected]> recipient ok
>>> RCPT TO:<[email protected]> NOTIFY=FAILURE \
   ORCPT=rfc822;[email protected]
<<< 250 <[email protected]> recipient ok
>>> RCPT TO:<[email protected]> NOTIFY=SUCCESS,FAILURE \
   ORCPT=rfc822;[email protected]
<<< 250 <[email protected]> recipient ok



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>>> RCPT TO:<[email protected]> NOTIFY=FAILURE \
   ORCPT=rfc822;[email protected]
<<< 250 <[email protected]> recipient ok
>>> RCPT TO:<[email protected]> NOTIFY=NEVER
<<< 250 <[email protected]> recipient ok
>>> RCPT TO:<[email protected]> NOTIFY=FAILURE \
   ORCPT=rfc822;[email protected]
<<< 250 <[email protected]> recipient ok
>>> DATA
<<< 354 okay, send message
>>> (message goes here)
>>> .
<<< 250 message accepted
>>> QUIT
<<< 221 goodbye

10.2 Relay to Big-Bucks.COM

  The SMTP at Pure-Heart.ORG then relays the message to Big-Bucks.COM.
  (For the purpose of this example, mail.Big-Bucks.COM is the primary
  mail exchanger for Big-Bucks.COM).

<<< 220 mail.Big-Bucks.COM says hello
>>> EHLO Pure-Heart.ORG
<<< 250-mail.Big-Bucks.COM
<<< 250 DSN
>>> MAIL FROM:<[email protected]> RET=HDRS ENVID=QQ314159
<<< 250 sender okay
>>> RCPT TO:<[email protected]> NOTIFY=SUCCESS \
   ORCPT=rfc822;[email protected]
<<< 250 recipient okay
>>> DATA
<<< 354 send message
>>> (message goes here)
>>> .
<<< 250 message received
>>> QUIT
<<< 221 bcnu

10.3 Relay to Ivory.EDU

  The SMTP at Pure-Heart.ORG relays the message to Ivory.EDU, which (as
  it happens) is a gateway to a LAN-based mail system that accepts SMTP
  mail and supports the DSN extension.

<<< 220 Ivory.EDU gateway to FooMail(tm) here
>>> EHLO Pure-Heart.ORG
<<< 250-Ivory.EDU



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<<< 250 DSN
>>> MAIL FROM:<[email protected]> RET=HDRS ENVID=QQ314159
<<< 250 ok
>>> RCPT TO:<[email protected]> NOTIFY=FAILURE \
   ORCPT=rfc822;[email protected]
<<< 550 error - no such recipient
>>> RCPT TO:<[email protected]> NOTIFY=SUCCESS,FAILURE \
   ORCPT=rfc822;[email protected]
<<< 250 recipient ok
>>> DATA
<<< 354 send message, end with '.'
>>> (message goes here)
>>> .
<<< 250 message received
>>> QUIT
<<< 221 bye

  Note that since the Ivory.EDU refused to accept mail for
  [email protected], and the sender specified NOTIFY=FAILURE, the
  sender-SMTP (in this case Pure-Heart.ORG) must generate a DSN.

10.4 Relay to Bombs.AF.MIL

  The SMTP at Pure-Heart.ORG relays the message to Bombs.AF.MIL, which
  does not support the SMTP extension.  Because the sender specified
  NOTIFY=NEVER for recipient [email protected], the SMTP at Pure-
  Heart.ORG chooses to send the message for that recipient in a
  separate transaction with a reverse-path of <>.

<<< 220-Bombs.AF.MIL reporting for duty.
<<< 220 Electronic mail is to be used for official business only.
>>> EHLO Pure-Heart.ORG
<<< 502 command not implemented
>>> RSET
<<< 250 reset
>>> HELO Pure-Heart.ORG
<<< 250 Bombs.AF.MIL
>>> MAIL FROM:<[email protected]>
<<< 250 ok
>>> RCPT TO:<[email protected]>
<<< 250 ok
>>> DATA
<<< 354 send message
>>> (message goes here)
>>> .
<<< 250 message accepted
>>> MAIL FROM:<>
<<< 250 ok



Moore                       Standards Track                    [Page 25]

RFC 1891           SMTP Delivery Status Notifications       January 1996


>>> RCPT TO:<[email protected]>
<<< 250 ok
>>> DATA
<<< 354 send message
>>> (message goes here)
>>> .
<<< 250 message accepted
>>> QUIT
<<< 221 Bombs.AF.MIL closing connection

10.5 Forward from [email protected] to [email protected]

  The SMTP at Pure-Heart.ORG relays the message to Tax-ME.GOV.  (this
  step is not shown).  MTA Tax-ME.GOV then forwards the message to
  [email protected] (shown below).  Both Tax-ME.GOV and Pure-Heart.ORG
  support the SMTP DSN extension.  Note that RET, ENVID, and ORCPT all
  retain their original values.

<<< 220 BoonDoggle.GOV says hello
>>> EHLO Pure-Heart.ORG
<<< 250-mail.Big-Bucks.COM
<<< 250 DSN
>>> MAIL FROM:<[email protected]> RET=HDRS ENVID=QQ314159
<<< 250 sender okay
>>> RCPT TO:<[email protected]> NOTIFY=SUCCESS \
   ORCPT=rfc822;[email protected]
<<< 250 recipient okay
>>> DATA
<<< 354 send message
>>> (message goes here)
>>> .
<<< 250 message received
>>> QUIT
<<< 221 bcnu

















Moore                       Standards Track                    [Page 26]

RFC 1891           SMTP Delivery Status Notifications       January 1996


10.6 "Delivered" DSN for [email protected]

  MTA mail.Big-Bucks.COM successfully delivers the message to Bob@Big-
  Bucks.COM.  Because the sender specified NOTIFY=SUCCESS, mail.Big-
  Bucks.COM issues the following DSN, and sends it to Alice@Pure-
  Heart.ORG.

To: [email protected]
From: [email protected]
Subject: Delivery Notification (success) for [email protected]
Content-Type: multipart/report; report-type=delivery-status;
   boundary=abcde
MIME-Version: 1.0

--abcde
Content-type: text/plain; charset=us-ascii

Your message (id QQ314159) was successfully delivered to
[email protected].

--abcde
Content-type: message/delivery-status

Reporting-MTA: dns; mail.Big-Bucks.COM
Original-Envelope-ID: QQ314159

Original-Recipient: rfc822;[email protected]
Final-Recipient: rfc822;[email protected]
Action: delivered
Status: 2.0.0

--abcde
Content-type: message/rfc822

(headers of returned message go here)

--abcde--














Moore                       Standards Track                    [Page 27]

RFC 1891           SMTP Delivery Status Notifications       January 1996


10.7 Failed DSN for [email protected]

  Because delivery to Carol failed and the sender specified
  NOTIFY=FAILURE for [email protected], MTA Pure-Heart.ORG (the SMTP
  client to which the failure was reported via SMTP) issues the
  following DSN.

To: [email protected]
From: [email protected]
Subject: Delivery Notification (failure) for [email protected]
Content-Type: multipart/report; report-type=delivery-status;
             boundary=bcdef
MIME-Version: 1.0

--bcdef
Content-type: text/plain; charset=us-ascii

Your message (id QQ314159) could not be delivered to
[email protected].

A transcript of the session follows:

(while talking to Ivory.EDU)
>>> RCPT TO:<[email protected]> NOTIFY=FAILURE
<<< 550 error - no such recipient

--bcdef
Content-type: message/delivery-status

Reporting-MTA: dns; Pure-Heart.ORG
Original-Envelope-ID: QQ314159

Original-Recipient: rfc822;[email protected]
Final-Recipient: rfc822;[email protected]
SMTP-Remote-Recipient: [email protected]
Diagnostic-Code: smtp; 550 error - no such recipient
Action: failed
Status: 5.0.0

--bcdef
Content-type: message/rfc822

(headers of returned message go here)

--bcdef--






Moore                       Standards Track                    [Page 28]

RFC 1891           SMTP Delivery Status Notifications       January 1996


10.8 Relayed DSN For [email protected]

  Although the mail gateway Ivory.EDU supports the DSN SMTP extension,
  the LAN mail system attached to its other side does not generate
  positive delivery confirmations.  So Ivory.EDU issues a "relayed"
  DSN:

To: [email protected]
From: [email protected]
Subject: mail relayed for [email protected]
Content-Type: multipart/report; report-type=delivery-status;
   boundary=cdefg
MIME-Version: 1.0

--cdefg
Content-type: text/plain; charset=us-ascii

Your message (addressed to [email protected]) was successfully
relayed to:

ymail!Dana

by the FooMail gateway at Ivory.EDU.

Unfortunately, the remote mail system does not support
confirmation of actual delivery.  Unless delivery to ymail!Dana
fails, this will be the only delivery status notification sent.

--cdefg
Content-type: message/delivery-status

Reporting-MTA: dns; Ivory.EDU
Original-Envelope-ID: QQ314159

Original-Recipient: rfc822;[email protected]
Final-Recipient: rfc822;[email protected]
Action: relayed
Status: 2.0.0

--cdefg
Content-type: message/rfc822

(headers of returned message go here)

--cdefg--






Moore                       Standards Track                    [Page 29]

RFC 1891           SMTP Delivery Status Notifications       January 1996


10.9 Failure notification for [email protected]

  The message originally addressed to [email protected] was forwarded
  to [email protected], but the MTA for Boondoggle.GOV was unable to
  deliver the message due to a lack of disk space in Sam's mailbox.
  After trying for several days, Boondoggle.GOV returned the following
  DSN:

To: [email protected]
From: [email protected]
Subject: Delivery failure for [email protected]
Content-Type: multipart/report; report-type=delivery-status;
             boundary=defgh
MIME-Version: 1.0

--defgh
Your message, originally addressed to [email protected], and forwarded
from there to [email protected] could not be delivered, for the
following reason:

write error to mailbox, disk quota exceeded

--defgh
Content-type: message/delivery-status

Reporting-MTA: Boondoggle.GOV
Original-Envelope-ID: QQ314159

Original-Recipient: rfc822;[email protected]
Final-Recipient: rfc822;[email protected]
Action: failed
Status: 4.2.2 (disk quota exceeded)

--defgh
Content-type: message/rfc822

(headers of returned message go here)

--defgh--












Moore                       Standards Track                    [Page 30]

RFC 1891           SMTP Delivery Status Notifications       January 1996


11. References

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

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

  [3] Westine, A., and J. Postel, "Problems with the Maintenance of
      Large Mailing Lists.", RFC 1211, USC/Information Sciences
      Institute, March 1991.

  [4] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker,
      "SMTP Service Extensions", RFC 1651, MCI, Innosoft, Dover Beach
      Consulting, Inc., Network Management Associates, Inc., Silicon
      Graphics, Inc., July 1994.

  [5] Moore, K., and G. Vaudreuil, "An Extensible Message Format for
      Delivery Status Notifications", RFC 1894, University of Tennessee,
      Octel Network Services, January 1996.

  [6] Crispin, M., "Internet Message Access Protocol - Version 4", RFC
      1730, University of Washington, 20 December 1994.

  [7] Myers, J., and M. Rose, "Post Office Protocol - Version 3", RFC
      1725, Carnegie Mellon, Dover Beach Consulting, November 1994.

  [8] Vaudreuil, G., "The Multipart/Report Content Type for the
      Reporting of Mail System Administrative Messages", RFC 1892, Octel
      Network Services, January 1996.

  [9] Braden, R., Editor, "Requirements for Internet Hosts - Application
      and Support", STD 3, RFC 1123, IETF, October 1989.

  [10] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893,
       Octel Network Services, January 1996.

12. Author's Address

  Keith Moore
  University of Tennessee
  107 Ayres Hall
  Knoxville, TN 37996-1301
  USA

  EMail: [email protected]





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