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rfc:rfc1891

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
 <notifications@cs.utk.edu>.  Requests to subscribe to the mailing
 list should be addressed to <notifications-request@cs.utk.edu>.
 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

Moore Standards Track [Page 1] RFC 1891 SMTP Delivery Status Notifications January 1996

 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,

© 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].

Moore Standards Track [Page 2] RFC 1891 SMTP Delivery Status Notifications January 1996

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

Moore Standards Track [Page 3] RFC 1891 SMTP Delivery Status Notifications January 1996

 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 A@B.C and later forwarded to A@D.E, after such forwarding has
  taken place, the RCPT command will specify a mailbox of A@D.E.
  However, the original recipient address remains A@B.C.
  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.

Moore Standards Track [Page 4] RFC 1891 SMTP Delivery Status Notifications January 1996

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,

Moore Standards Track [Page 5] RFC 1891 SMTP Delivery Status Notifications January 1996

 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:

Moore Standards Track [Page 6] RFC 1891 SMTP Delivery Status Notifications January 1996

   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.

Moore Standards Track [Page 7] RFC 1891 SMTP Delivery Status Notifications January 1996

 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

Moore Standards Track [Page 8] RFC 1891 SMTP Delivery Status Notifications January 1996

 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".

Moore Standards Track [Page 9] RFC 1891 SMTP Delivery Status Notifications January 1996

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.

Moore Standards Track [Page 10] RFC 1891 SMTP Delivery Status Notifications January 1996

© 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.

© 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.

Moore Standards Track [Page 11] RFC 1891 SMTP Delivery Status Notifications January 1996

  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.

© If the NOTIFY parameter was not supplied for that recipient, the MTA

  MUST NOT issue a DSN.

Moore Standards Track [Page 12] RFC 1891 SMTP Delivery Status Notifications January 1996

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.

© 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.

Moore Standards Track [Page 13] RFC 1891 SMTP Delivery Status Notifications January 1996

© 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.

© 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.

Moore Standards Track [Page 14] RFC 1891 SMTP Delivery Status Notifications January 1996

 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.

© 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

Moore Standards Track [Page 15] RFC 1891 SMTP Delivery Status Notifications January 1996

  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.)

© 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.

Moore Standards Track [Page 16] RFC 1891 SMTP Delivery Status Notifications January 1996

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

Moore Standards Track [Page 17] RFC 1891 SMTP Delivery Status Notifications January 1996

 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].

Moore Standards Track [Page 18] RFC 1891 SMTP Delivery Status Notifications January 1996

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.

© 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.

Moore Standards Track [Page 19] RFC 1891 SMTP Delivery Status Notifications January 1996

(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.

Moore Standards Track [Page 20] RFC 1891 SMTP Delivery Status Notifications January 1996

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.

© 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

Moore Standards Track [Page 21] RFC 1891 SMTP Delivery Status Notifications January 1996

  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

© 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].

Moore Standards Track [Page 22] RFC 1891 SMTP Delivery Status Notifications January 1996

© 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 Alice@Pure-Heart.ORG to
 Bob@Big-Bucks.COM, Carol@Ivory.EDU, Dana@Ivory.EDU,
 Eric@Bombs.AF.MIL, Fred@Bombs.AF.MIL, and George@Tax-ME.GOV, 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:Alice@Pure-Heart.ORG RET=HDRS ENVID=QQ314159

«< 250 Alice@Pure-Heart.ORG sender ok

RCPT TO:Bob@Big-Bucks.COM NOTIFY=SUCCESS \
  ORCPT=rfc822;Bob@Big-Bucks.COM

«< 250 Bob@Big-Bucks.COM recipient ok
RCPT TO:Carol@Ivory.EDU NOTIFY=FAILURE \

  ORCPT=rfc822;Carol@Ivory.EDU

«< 250 Carol@Ivory.EDU recipient ok
RCPT TO:Dana@Ivory.EDU NOTIFY=SUCCESS,FAILURE \

  ORCPT=rfc822;Dana@Ivory.EDU

«< 250 Dana@Ivory.EDU recipient ok

Moore Standards Track [Page 23] RFC 1891 SMTP Delivery Status Notifications January 1996

RCPT TO:Eric@Bombs.AF.MIL NOTIFY=FAILURE \
  ORCPT=rfc822;Eric@Bombs.AF.MIL

«< 250 Eric@Bombs.AF.MIL recipient ok
RCPT TO:Fred@Bombs.AF.MIL NOTIFY=NEVER

«< 250 Fred@Bombs.AF.MIL recipient ok

RCPT TO:George@Tax-ME.GOV NOTIFY=FAILURE \
  ORCPT=rfc822;George@Tax-ME.GOV

«< 250 George@Tax-ME.GOV 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:Alice@Pure-Heart.ORG RET=HDRS ENVID=QQ314159

«< 250 sender okay

RCPT TO:Bob@Big-Bucks.COM NOTIFY=SUCCESS \
  ORCPT=rfc822;Bob@Big-Bucks.COM

«< 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™ here

EHLO Pure-Heart.ORG

«< 250-Ivory.EDU

Moore Standards Track [Page 24] RFC 1891 SMTP Delivery Status Notifications January 1996

«< 250 DSN

MAIL FROM:Alice@Pure-Heart.ORG RET=HDRS ENVID=QQ314159

«< 250 ok

RCPT TO:Carol@Ivory.EDU NOTIFY=FAILURE \
  ORCPT=rfc822;Carol@Ivory.EDU

«< 550 error - no such recipient
RCPT TO:Dana@Ivory.EDU NOTIFY=SUCCESS,FAILURE \

  ORCPT=rfc822;Dana@Ivory.EDU

«< 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
 Carol@Ivory.EDU, 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 Fred@Bombs.AF.MIL, 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

«< 250 ok

«< 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

«< 250 ok

DATA

«< 354 send message

(message goes here)
.

«< 250 message accepted

QUIT

«< 221 Bombs.AF.MIL closing connection

10.5 Forward from George@Tax-ME.GOV to Sam@Boondoggle.GOV

 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
 Sam@Boondoggle.GOV (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:Alice@Pure-Heart.ORG RET=HDRS ENVID=QQ314159

«< 250 sender okay

RCPT TO:Sam@Boondoggle.GOV NOTIFY=SUCCESS \
  ORCPT=rfc822;George@Tax-ME.GOV

«< 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 Bob@Big-Bucks.COM

 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: Alice@Pure-Heart.ORG From: postmaster@mail.Big-Bucks.COM Subject: Delivery Notification (success) for Bob@Big-Bucks.COM 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 Bob@Big-Bucks.COM.

–abcde Content-type: message/delivery-status

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

Original-Recipient: rfc822;Bob@Big-Bucks.COM Final-Recipient: rfc822;Bob@Big-Bucks.COM 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 Carol@Ivory.EDU

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

To: Alice@Pure-Heart.ORG From: postmaster@Pure-Heart.ORG Subject: Delivery Notification (failure) for Carol@Ivory.EDU 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 Carol@Ivory.EDU.

A transcript of the session follows:

(while talking to Ivory.EDU)

RCPT TO:Carol@Ivory.EDU 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;Carol@Ivory.EDU Final-Recipient: rfc822;Carol@Ivory.EDU SMTP-Remote-Recipient: Carol@Ivory.EDU 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 Dana@Ivory.EDU

 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: Alice@Pure-Heart.ORG From: postmaster@Ivory.EDU Subject: mail relayed for Dana@Ivory.EDU 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 Dana@Ivory.EDU) 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;Dana@Ivory.EDU Final-Recipient: rfc822;Dana@Ivory.EDU 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 Sam@Boondoggle.GOV

 The message originally addressed to George@Tax-ME.GOV was forwarded
 to Sam@Boondoggle.GOV, 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: Alice@BigHeart.ORG From: Postmaster@Boondoggle.GOV Subject: Delivery failure for Sam@Boondoggle.GOV Content-Type: multipart/report; report-type=delivery-status;

            boundary=defgh

MIME-Version: 1.0

–defgh Your message, originally addressed to George@Tax-ME.GOV, and forwarded from there to Sam@Boondoggle.GOV 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;George@Tax-ME.GOV Final-Recipient: rfc822;Sam@Boondoggle.GOV 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: moore@cs.utk.edu

Moore Standards Track [Page 31]

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