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rfc:rfc3461

Network Working Group K. Moore Request for Comments: 3461 University of Tennessee Obsoletes 1891 January 2003 Category: Standards Track

       Simple Mail Transfer Protocol (SMTP) Service Extension
              for Delivery Status Notifications (DSNs)

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.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 This memo defines an extension to the Simple Mail Transfer Protocol
 (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.

Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in BCP 14, RFC 2119 [7].

Table of Contents

 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2. Framework for the Delivery Status Notification Extension . . .  4
 3. The Delivery Status Notification service extension . . . . . .  5
 4. Additional parameters for RCPT and MAIL commands . . . . . . .  6
 4.1 The NOTIFY parameter of the ESMTP RCPT command. . . . . . . .  7
 4.2 The ORCPT parameter to the ESMTP RCPT command . . . . . . . .  8
 4.3 The RET parameter of the ESMTP MAIL command . . . . . . . . .  9
 4.4 The ENVID parameter to the ESMTP MAIL command . . . . . . . .  9

Moore Standards Track [Page 1] RFC 3461 SMTP DSN Extension January 2003

 4.5 Restrictions on the use of Delivery Status Notification
     parameters. . . . . . . . . . . . . . . . . . . . . . . . . . 10
 5. Conformance requirements . . . . . . . . . . . . . . . . . . . 10
 5.1 SMTP protocol interactions. . . . . . . . . . . . . . . . . . 11
 5.2 Handling of messages received via SMTP. . . . . . . . . . . . 11
 5.2.1 Relay of messages to other conforming SMTP servers. . . . . 12
 5.2.2 Relay of messages to non-conforming SMTP servers. . . . . . 13
 5.2.3 Local delivery of messages. . . . . . . . . . . . . . . . . 14
 5.2.4 Gatewaying a message into a foreign environment . . . . . . 14
 5.2.5 Delays in delivery. . . . . . . . . . . . . . . . . . . . . 15
 5.2.6 Failure of a conforming MTA to deliver a message. . . . . . 16
 5.2.7 Forwarding, aliases, and mailing lists. . . . . . . . . . . 16
 5.2.7.1 mailing lists . . . . . . . . . . . . . . . . . . . . . . 17
 5.2.7.2 single-recipient aliases. . . . . . . . . . . . . . . . . 18
 5.2.7.3 multiple-recipient aliases. . . . . . . . . . . . . . . . 18
 5.2.7.4 confidential forwarding addresses . . . . . . . . . . . . 18
 5.2.8 DSNs describing delivery to multiple recipients . . . . . . 19
 5.3 Handling of messages from other sources . . . . . . . . . . . 19
 5.4 Implementation limits . . . . . . . . . . . . . . . . . . . . 19
 6. Format of delivery notifications . . . . . . . . . . . . . . . 20
 6.1 SMTP Envelope to be used with delivery status
     notifications . . . . . . . . . . . . . . . . . . . . . . . . 20
 6.2 Contents of the DSN . . . . . . . . . . . . . . . . . . . . . 20
 6.3 Message/delivery-status fields. . . . . . . . . . . . . . . . 21
 7. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 22
 8. Security Considerations. . . . . . . . . . . . . . . . . . . . 22
 9. Appendix - Type-Name Definitions . . . . . . . . . . . . . . . 24
 9.1 "rfc822" address-type . . . . . . . . . . . . . . . . . . . . 24
 9.2 "smtp" diagnostic-type. . . . . . . . . . . . . . . . . . . . 24
 9.3 "dns" MTA-name-type . . . . . . . . . . . . . . . . . . . . . 25
 10. Appendix - Example. . . . . . . . . . . . . . . . . . . . . . 26
 10.1 Submission . . . . . . . . . . . . . . . . . . . . . . . . . 27
 10.2 Relay to Example.COM . . . . . . . . . . . . . . . . . . . . 28
 10.3 Relay to Ivory.EDU . . . . . . . . . . . . . . . . . . . . . 29
 10.4 Relay to Bombs.AF.MIL. . . . . . . . . . . . . . . . . . . . 30
 10.5 Forward from George@Tax-ME.GOV to Sam@Boondoggle.GOV . . . . 31
 10.6 "Delivered" DSN for Bob@Example.COM. . . . . . . . . . . . . 32
 10.7 Failed DSN for Carol@Ivory.EDU . . . . . . . . . . . . . . . 33
 10.8 Relayed DSN For Dana@Ivory.EDU . . . . . . . . . . . . . . . 34
 10.9 Failure notification for Sam@Boondoggle.GOV. . . . . . . . . 35
 11. Appendix - Changes since RFC 1891 . . . . . . . . . . . . . . 35
 12. References. . . . . . . . . . . . . . . . . . . . . . . . . . 36
 12.1 Normative References . . . . . . . . . . . . . . . . . . . . 36
 12.2 Informative References . . . . . . . . . . . . . . . . . . . 36
 13. Author's Address. . . . . . . . . . . . . . . . . . . . . . . 37
 14. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 38

Moore Standards Track [Page 2] RFC 3461 SMTP DSN Extension January 2003

1. 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
 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 [8] 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.

Moore Standards Track [Page 3] RFC 3461 SMTP DSN Extension January 2003

 In an attempt to provide such a service, this memo uses the mechanism
 defined in [1] 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 [3].

2. 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 3 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 4.4;
 (5)  no additional SMTP verbs are defined by this extension.
 The remainder of this memo specifies how support for the extension
 affects the behavior of a message transfer agent.

Moore Standards Track [Page 4] RFC 3461 SMTP DSN Extension January 2003

3. 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
 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 for Delivery Status Notifications to be meaningful to the
 sender, ESMTP servers, which support this extension, should propagate
 the following information for use in generating DSNs to any other
 MTAs that are used to relay the message:
 (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.

Moore Standards Track [Page 5] RFC 3461 SMTP DSN Extension January 2003

      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.

4. 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 [1].
 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 [1] 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.)

Moore Standards Track [Page 6] RFC 3461 SMTP DSN Extension January 2003

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

4.1 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,
 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.

Moore Standards Track [Page 7] RFC 3461 SMTP DSN Extension January 2003

 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.

4.2 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:
    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 [3]), 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.

Moore Standards Track [Page 8] RFC 3461 SMTP DSN Extension January 2003

 Due to limitations in the Delivery Status Notification format, the
 value of the original recipient address prior to encoding as "xtext"
 MUST consist entirely of printable (graphic and white space)
 characters from the US-ASCII [4] repertoire.  If an addr-type is
 defined for addresses which use characters outside of this
 repertoire, the specification for that addr-type MUST define the
 means of encoding those addresses in printable US-ASCII characters
 when are then encoded as xtext.

4.3 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.
 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.

4.4 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.

Moore Standards Track [Page 9] RFC 3461 SMTP DSN Extension January 2003

 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.
 Due to limitations in the Delivery Status Notification format, the
 value of the ENVID parameter prior to encoding as "xtext" MUST
 consist entirely of printable (graphic and white space) characters
 from the US-ASCII [4] repertoire.

4.5 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".

5. 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
 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.

Moore Standards Track [Page 10] RFC 3461 SMTP DSN Extension January 2003

5.1 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".

5.2 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

Moore Standards Track [Page 11] RFC 3461 SMTP DSN Extension January 2003

 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.

5.2.1 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.
 (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.)

Moore Standards Track [Page 12] RFC 3461 SMTP DSN Extension January 2003

     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.

5.2.2 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.
     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].

Moore Standards Track [Page 13] RFC 3461 SMTP DSN Extension January 2003

 (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.

5.2.3 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 [9], POP [10] 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.

5.2.4 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

Moore Standards Track [Page 14] RFC 3461 SMTP DSN Extension January 2003

     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.

5.2.5 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.
 (c)  If the NOTIFY parameter was supplied which did not contain the
      DELAY keyword, a "delayed" DSN MUST NOT be issued.

Moore Standards Track [Page 15] RFC 3461 SMTP DSN Extension January 2003

 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.

5.2.6 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".

5.2.7 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.
 Following the example of [11] (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

Moore Standards Track [Page 16] RFC 3461 SMTP DSN Extension January 2003

 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:

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

Moore Standards Track [Page 17] RFC 3461 SMTP DSN Extension January 2003

5.2.7.2 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.

5.2.7.3 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.

5.2.7.4 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 18] RFC 3461 SMTP DSN Extension January 2003

5.2.8 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.

5.3 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.

5.4 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 19] RFC 3461 SMTP DSN Extension January 2003

 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.

6. Format of delivery notifications

 The format of Delivery Status Notifications is defined in [3], which
 uses the framework defined in [5].  Delivery Status Notifications are
 to be returned to the sender of the original message as outlined
 below.

6.1 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 [11].  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.

6.2 Contents of the DSN

 A DSN is transmitted as a MIME message with a top-level content-type
 of multipart/report (as defined in [3]).
 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 [5], 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 [3]).  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 [5].

Moore Standards Track [Page 20] RFC 3461 SMTP DSN Extension January 2003

6.3 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 [3] 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 [3] 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 21] RFC 3461 SMTP DSN Extension January 2003

 (g)  The Status field MUST be supplied, using a status-code from [6].
      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 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 recipient which was presented to the remote SMTP
      server.
 (k)  Other per-recipient fields defined in [3] MAY appear, as
      appropriate.

7. 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.

8. Security Considerations

 The SMTP extension described in this document does not change the
 fundamental nature of the SMTP service and hence does not create any
 new security exposures in and of itself.  It necessarily adds
 complexity to implementations, however, and with added complexity
 comes an increased risk of implementation errors.
 Previous ad-hoc delivery notification mechanisms sometimes produced a
 storm of receipts due to unanticipated interactions with mailing list
 expansion software.  In this specification notification of successful
 delivery is carefully designed so, if properly implemented, it cannot
 interact with a list expander in this way.

Moore Standards Track [Page 22] RFC 3461 SMTP DSN Extension January 2003

 The security considerations section in [5] describes security issues
 associated with multipart/report objects in general and the security
 considerations section in [3] describes security issues with DSNs in
 particular.

Moore Standards Track [Page 23] RFC 3461 SMTP DSN Extension January 2003

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

Moore Standards Track [Page 24] RFC 3461 SMTP DSN Extension January 2003

      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] and [11].
      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 25] RFC 3461 SMTP DSN Extension January 2003

 (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 Alice@Example.ORG to
 Bob@Example.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.

Moore Standards Track [Page 26] RFC 3461 SMTP DSN Extension January 2003

10.1 Submission

 Alice's user agent sends the message to the SMTP server at
 Example.ORG.  Note that while this example uses SMTP as a mail
 submission protocol, other protocols could also be used.
    <<< 220 Example.ORG SMTP server here
    >>> EHLO Example.ORG
    <<< 250-Example.ORG
    <<< 250-DSN
    <<< 250-EXPN
    <<< 250 SIZE
    >>> MAIL FROM:<Alice@Example.ORG> RET=HDRS ENVID=QQ314159
    <<< 250 <Alice@Example.ORG> sender ok
    >>> RCPT TO:<Bob@Example.COM> NOTIFY=SUCCESS \
        ORCPT=rfc822;Bob@Example.COM
    <<< 250 <Bob@Example.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
    >>> 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

Moore Standards Track [Page 27] RFC 3461 SMTP DSN Extension January 2003

10.2 Relay to Example.COM

 The SMTP at Example.ORG then relays the message to Example.COM.  (For
 the purpose of this example, mail.Example.COM is the primary mail
 exchanger for Example.COM).
    <<< 220 mail.Example.COM says hello
    >>> EHLO Example.ORG
    <<< 250-mail.Example.COM
    <<< 250 DSN
    >>> MAIL FROM:<Alice@Example.ORG> RET=HDRS ENVID=QQ314159
    <<< 250 sender okay
    >>> RCPT TO:<Bob@Example.COM> NOTIFY=SUCCESS \
        ORCPT=rfc822;Bob@Example.COM
    <<< 250 recipient okay
    >>> DATA
    <<< 354 send message
    >>> (message goes here)
    >>> .
    <<< 250 message received
    >>> QUIT
    <<< 221 bcnu

Moore Standards Track [Page 28] RFC 3461 SMTP DSN Extension January 2003

10.3 Relay to Ivory.EDU

 The SMTP at Example.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 Example.ORG
    <<< 250-Ivory.EDU
    <<< 250 DSN
    >>> MAIL FROM:<Alice@Example.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 Example.ORG) must generate a DSN.

Moore Standards Track [Page 29] RFC 3461 SMTP DSN Extension January 2003

10.4 Relay to Bombs.AF.MIL

 The SMTP at Example.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 Example.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 Example.ORG
    <<< 502 command not implemented
    >>> RSET
    <<< 250 reset
    >>> HELO Example.ORG
    <<< 250 Bombs.AF.MIL
    >>> MAIL FROM:<Alice@Example.ORG>
    <<< 250 ok
    >>> RCPT TO:<Eric@Bombs.AF.MIL>
    <<< 250 ok
    >>> DATA
    <<< 354 send message
    >>> (message goes here)
    >>> .
    <<< 250 message accepted
    >>> MAIL FROM:<>
    <<< 250 ok
    >>> RCPT TO:<Fred@Bombs.AF.MIL>
    <<< 250 ok
    >>> DATA
    <<< 354 send message
    >>> (message goes here)
    >>> .
    <<< 250 message accepted
    >>> QUIT
    <<< 221 Bombs.AF.MIL closing connection

Moore Standards Track [Page 30] RFC 3461 SMTP DSN Extension January 2003

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

 The SMTP at Example.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 Example.ORG
 support the SMTP DSN extension.  Note that RET, ENVID, and ORCPT all
 retain their original values.
    <<< 220 BoonDoggle.GOV says hello
    >>> EHLO Example.ORG
    <<< 250-mail.Example.COM
    <<< 250 DSN
    >>> MAIL FROM:<Alice@Example.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 31] RFC 3461 SMTP DSN Extension January 2003

10.6 "Delivered" DSN for Bob@Example.COM

 MTA mail.Example.COM successfully delivers the message to
 Bob@Example.COM.  Because the sender specified NOTIFY=SUCCESS,
 mail.Example.COM issues the following DSN, and sends it to
 Alice@Example.ORG.
    To: Alice@Example.ORG
    From: postmaster@mail.Example.COM
    Subject: Delivery Notification (success) for Bob@Example.COM
    Content-Type: multipart/report; report-type=delivery-status;
        boundary=abcde
    MIME-Version: 1.0
  1. -abcde

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

    Your message (id QQ314159) was successfully delivered to
    Bob@Example.COM.
  1. -abcde

Content-type: message/delivery-status

    Reporting-MTA: dns; mail.Example.COM
    Original-Envelope-ID: QQ314159
    Original-Recipient: rfc822;Bob@Example.COM
    Final-Recipient: rfc822;Bob@Example.COM
    Action: delivered
    Status: 2.0.0
  1. -abcde

Content-type: message/rfc822

    (headers of returned message go here)
  1. -abcde–

Moore Standards Track [Page 32] RFC 3461 SMTP DSN Extension January 2003

10.7 Failed DSN for Carol@Ivory.EDU

 Because delivery to Carol failed and the sender specified
 NOTIFY=FAILURE for Carol@Ivory.EDU, MTA Example.ORG (the SMTP client
 to which the failure was reported via SMTP) issues the following DSN.
    To: Alice@Example.ORG
    From: postmaster@Example.ORG
    Subject: Delivery Notification (failure) for Carol@Ivory.EDU
    Content-Type: multipart/report; report-type=delivery-status;
                  boundary=bcdef
    MIME-Version: 1.0
  1. -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
  1. -bcdef

Content-type: message/delivery-status

    Reporting-MTA: dns; Example.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
  1. -bcdef

Content-type: message/rfc822

    (headers of returned message go here)
  1. -bcdef–

Moore Standards Track [Page 33] RFC 3461 SMTP DSN Extension January 2003

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@Example.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
  1. -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.
  1. -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
  1. -cdefg

Content-type: message/rfc822

    (headers of returned message go here)
  1. -cdefg–

Moore Standards Track [Page 34] RFC 3461 SMTP DSN Extension January 2003

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@Example.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
  1. -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
  1. -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)
  1. -defgh

Content-type: message/rfc822

    (headers of returned message go here)
  1. -defgh–

11. Appendix - Changes since RFC 1891

  1. updated author's address
  1. In examples, changed Pure-Heart.ORG and Big-Bucks.COM to

Example.ORG and Example.COM, respectively. Since publication

         of RFC 1891, the former two domains have been registered.

Moore Standards Track [Page 35] RFC 3461 SMTP DSN Extension January 2003

  1. Clarified that ENVID and ORCPT parameters must consist

entirely of US-ASCII characters prior to encoding as xtext.

  1. A Security Considerations section was added.

12. References

12.1 Normative References

 [1]  Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
      August 1982.
 [2]  Crocker, D., "Standard for the format of ARPA Internet Text
      Messages", STD 11, RFC 822, August 1982.
 [3]  Moore, K., and G. Vaudreuil, "An Extensible Message Format for
      Delivery Status Notifications", RFC 3464, January 2003.
 [4]  Coded Character Set - 7-Bit American Standard Code for
      Information Interchange, ANSI X3.4-1986.
 [5]  Vaudreuil, G., "The Multipart/Report Content Type for the
      Reporting of Mail System Administrative Messages", RFC 3462,
      January 2003.
 [6]  Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 3463,
      January 2003.
 [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

12.2 Informative References

 [8]  Westine, A. and J. Postel, "Problems with the Maintenance of
      Large Mailing Lists.", RFC 1211, March 1991.
 [9]  Crispin, M., "Internet Message Access Protocol - Version 4rev1",
      RFC 2060, December 1996.
 [10] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD
      53, RFC 1939, May 1996.
 [11] Braden, R., Ed., "Requirements for Internet Hosts - Application
      and Support", STD 3, RFC 1123, October 1989.

Moore Standards Track [Page 36] RFC 3461 SMTP DSN Extension January 2003

13. Author's Address

 Keith Moore
 University of Tennessee
 1122 Volunteer Blvd, Suite 203
 Knoxville, TN 37996-3450
 USA
 EMail: moore@cs.utk.edu

Moore Standards Track [Page 37] RFC 3461 SMTP DSN Extension January 2003

14. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Moore Standards Track [Page 38]

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