Network Working Group K. Moore
Request for Comments: 1894 University of Tennessee
Category: Standards Track G. Vaudreuil
Octel Network Services
January 1996
An Extensible Message Format 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.
Abstract
This memo defines a MIME content-type that may be used by a message
transfer agent (MTA) or electronic mail gateway to report the result
of an attempt to deliver a message to one or more recipients. This
content-type is intended as a machine-processable replacement for the
various types of delivery status notifications currently used in
Internet electronic mail.
Because many messages are sent between the Internet and other
messaging systems (such as X.400 or the so-called "LAN-based"
systems), the DSN protocol is designed to be useful in a multi-
protocol messaging environment. To this end, the protocol described
in this memo provides for the carriage of "foreign" addresses and
error codes, in addition to those normally used in Internet mail.
Additional attributes may also be defined to support "tunneling" of
foreign notifications through Internet mail.
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
. Requests to subscribe to the mailing
list should be addressed to .
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
Moore & Vaudreuil Standards Track [Page 1]
RFC 1894 Delivery Status Notifications January 1996
experience, and are thus subject to change.
1. Introduction
This memo defines a MIME [1] content-type for delivery status
notifications (DSNs). A DSN can be used to notify the sender of a
message of any of several conditions: failed delivery, delayed
delivery, successful delivery, or the gatewaying of a message into an
environment that may not support DSNs. The "message/delivery-status"
content-type defined herein is intended for use within the framework
of the "multipart/report" content type defined in [2].
This memo defines only the format of the notifications. An extension
to the Simple Message Transfer Protocol (SMTP) [3] to fully support
such notifications is the subject of a separate memo [4].
1.1 Purposes
The DSNs defined in this memo are expected to serve several purposes:
(a) Inform human beings of the status of message delivery processing, as
well as the reasons for any delivery problems or outright failures,
in a manner which is largely independent of human language;
(b) Allow mail user agents to keep track of the delivery status of
messages sent, by associating returned DSNs with earlier message
transmissions;
(c) Allow mailing list exploders to automatically maintain their
subscriber lists when delivery attempts repeatedly fail;
(d) Convey delivery and non-delivery notifications resulting from
attempts to deliver messages to "foreign" mail systems via a
gateway;
(e) Allow "foreign" notifications to be tunneled through a MIME-capable
message system and back into the original messaging system that
issued the original notification, or even to a third messaging
system;
(f) Allow language-independent, yet reasonably precise, indications of
the reason for the failure of a message to be delivered (once status
codes of sufficient precision are defined); and
(g) Provide sufficient information to remote MTA maintainers (via
"trouble tickets") so that they can understand the nature of
reported errors. This feature is used in the case that failure to
deliver a message is due to the malfunction of a remote MTA and the
Moore & Vaudreuil Standards Track [Page 2]
RFC 1894 Delivery Status Notifications January 1996
sender wants to report the problem to the remote MTA administrator.
1.2 Requirements
These purposes place the following constraints on the notification
protocol:
(a) It must be readable by humans as well as being machine-parsable.
(b) It must provide enough information to allow message senders (or the
user agents) to unambiguously associate a DSN with the message that
was sent and the original recipient address for which the DSN is
issued (if such information is available), even if the message was
forwarded to another recipient address.
(c) It must be able to preserve the reason for the success or failure of
a delivery attempt in a remote messaging system, using the
"language" (mailbox addresses and status codes) of that remote
system.
(d) It must also be able to describe the reason for the success or
failure of a delivery attempt, independent of any particular human
language or of the "language" of any particular mail system.
(e) It must preserve enough information to allow the maintainer of a
remote MTA to understand (and if possible, reproduce) the conditions
that caused a delivery failure at that MTA.
(f) For any notifications issued by foreign mail systems, which are
translated by a mail gateway to the DSN format, the DSN must
preserve the "type" of the foreign addresses and error codes, so
that these may be correctly interpreted by gateways.
A DSN contains a set of per-message fields which identify the message
and the transaction during which the message was submitted, along
with other fields that apply to all delivery attempts described by
the DSN. The DSN also includes a set of per-recipient fields to
convey the result of the attempt to deliver the message to each of
one or more recipients.
1.3 Terminology
A message may be transmitted through several message transfer agents
(MTAs) on its way to a recipient. For a variety of reasons,
recipient addresses may be rewritten during this process, so each MTA
may potentially see a different recipient address. Depending on the
purpose for which a DSN is used, different formats of a particular
recipient address will be needed.
Moore & Vaudreuil Standards Track [Page 3]
RFC 1894 Delivery Status Notifications January 1996
Several DSN fields are defined in terms of the view from a particular
MTA in the transmission. The MTAs are assigned the following names:
(a) Original MTA
The Original MTA is the one to which the message is submitted for
delivery by the sender of the message.
(b) Reporting MTA
For any DSN, the Reporting MTA is the one which is reporting the
results of delivery attempts described in the DSN.
If the delivery attempts described occurred in a "foreign" (non-
Internet) mail system, and the DSN was produced by translating the
foreign notice into DSN format, the Reporting MTA will still identify
the "foreign" MTA where the delivery attempts occurred.
(c) Received-From MTA
The Received-From MTA is the MTA from which the Reporting MTA
received the message, and accepted responsibility for delivery of the
message.
(d) Remote MTA
If an MTA determines that it must relay a message to one or more
recipients, but the message cannot be transferred to its "next hop"
MTA, or if the "next hop" MTA refuses to accept responsibility for
delivery of the message to one or more of its intended recipients,
the relaying MTA may need to issue a DSN on behalf of the recipients
for whom the message cannot be delivered. In this case the relaying
MTA is the Reporting MTA, and the "next hop" MTA is known as the
Remote MTA.
Moore & Vaudreuil Standards Track [Page 4]
RFC 1894 Delivery Status Notifications January 1996
Figure 1 illustrates the relationship between the various MTAs.
+-----+ +--------+ +---------+ +---------+ +------+
| | | | |Received-| | | | |
| | => |Original| => ... => | From | => |Reporting| ===> |Remote|
| user| | MTA | | MTA | | MTA | ".
A particular DSN describes the delivery status for exactly one
message. However, an MTA MAY report on the delivery status for
several recipients of the same message in a single DSN. Due to the
nature of the mail transport system (where responsibility for
delivery of a message to its recipients may be split among several
MTAs, and delivery to any particular recipient may be delayed),
multiple DSNs may be still be issued in response to a single message
submission.
Moore & Vaudreuil Standards Track [Page 7]
RFC 1894 Delivery Status Notifications January 1996
2.1 The message/delivery-status content-type
The message/delivery-status content-type is defined as follows:
MIME type name: message
MIME subtype name: delivery-status
Optional parameters: none
Encoding considerations: "7bit" encoding is sufficient and
MUST be used to maintain readability
when viewed by non-MIME mail
readers.
Security considerations: discussed in section 4 of this memo.
The message/delivery-status report type for use in the
multipart/report is "delivery-status".
The body of a message/delivery-status consists of one or more
"fields" formatted according to the ABNF of RFC 822 header "fields"
(see [6]). The per-message fields appear first, followed by a blank
line. Following the per-message fields are one or more groups of
per-recipient fields. Each group of per-recipient fields is preceded
by a blank line. Using the ABNF of RFC 822, the syntax of the
message/delivery-status content is as follows:
delivery-status-content =
per-message-fields 1*( CRLF per-recipient-fields )
The per-message fields are described in section 2.2. The per-
recipient fields are described in section 2.3.
2.1.1 General conventions for DSN fields
Since these fields are defined according to the rules of RFC 822, the
same conventions for continuation lines and comments apply.
Notification fields may be continued onto multiple lines by beginning
each additional line with a SPACE or HTAB. Text which appears in
parentheses is considered a comment and not part of the contents of
that notification field. Field names are case-insensitive, so the
names of notification fields may be spelled in any combination of
upper and lower case letters. Comments in DSN fields may use the
"encoded-word" construct defined in [7].
A number of DSN fields are defined to have a portion of a field body
of "xtext". "xtext" is used to allow encoding sequences of octets
which contain values outside the range [1-127 decimal] of traditional
ASCII characters, and also to allow comments to be inserted in the
data. Any octet may be encoded as "+" followed by two upper case
Moore & Vaudreuil Standards Track [Page 8]
RFC 1894 Delivery Status Notifications January 1996
hexadecimal digits. (The "+" character MUST be encoded as "+2B".)
With certain exceptions, octets that correspond to ASCII characters
may be represented as themselves. SPACE and HTAB characters are
ignored. Comments may be included by enclosing them in parenthesis.
Except within comments, encoded-words such as defined in [7] may NOT
be used in xtext.
"xtext" is formally defined as follows:
xtext = *( xchar / hexchar / linear-white-space / comment )
xchar = any ASCII CHAR between "!" (33) and "~" (126) inclusive,
except for "+", "\" and "(".
"hexchar"s are intended to encode octets that cannot be represented
as plain text, either because they are reserved, or because they are
non-printable. However, any octet value may be represented by a
"hexchar".
hexchar = ASCII "+" immediately followed by two upper case
hexadecimal digits
When encoding an octet sequence as xtext:
+ Any ASCII CHAR between "!" and "~" inclusive, except for "+", "\",
and "(", MAY be encoded as itself. (Some CHARs in this range may
also be encoded as "hexchar"s, at the implementor's discretion.)
+ ASCII CHARs that fall outside the range above must be encoded as
"hexchar".
+ Line breaks (CR LF SPACE) MAY be inserted as necessary to keep line
lengths from becoming excessive.
+ Comments MAY be added to clarify the meaning for human readers.
2.1.2 "*-type" subfields
Several DSN fields consist of a "-type" subfield, followed by a
semicolon, followed by "*text". For these fields, the keyword used
in the address-type, diagnostic-type, or MTA-name-type subfield
indicates the expected format of the address, status-code, or MTA-
name which follows.
Moore & Vaudreuil Standards Track [Page 9]
RFC 1894 Delivery Status Notifications January 1996
The "-type" subfields are defined as follows:
(a) An "address-type" specifies the format of a mailbox address. For
example, Internet mail addresses use the "rfc822" address-type.
address-type = atom
(b) A "diagnostic-type" specifies the format of a status code. For
example, when a DSN field contains a reply code reported via the
Simple Mail Transfer Protocol [3], the "smtp" diagnostic-type is
used.
diagnostic-type = atom
(c) An "MTA-name-type" specifies the format of an MTA name. For
example, for an SMTP server on an Internet host, the MTA name is the
domain name of that host, and the "dns" MTA-name-type is used.
mta-name-type = atom
Values for address-type, diagnostic-type, and MTA-name-type are
case-insensitive. Thus address-type values of "RFC822" and "rfc822"
are equivalent.
The Internet Assigned Numbers Authority (IANA) will maintain a
registry of address-types, diagnostic-types, and MTA-name-types,
along with descriptions of the meanings and acceptable values of
each, or a reference to a one or more specifications that provide
such descriptions. (The "rfc822" address-type, "smtp" diagnostic-
type, and "dns" MTA-name-type are defined in [4].) Registration
forms for address-type, diagnostic-type, and MTA-name-type appear in
section 8 of this document.
IANA will not accept registrations for any address-type, diagnostic-
type, or MTA-name-type name that begins with "X-". These type names
are reserved for experimental use.
2.1.3 Lexical tokens imported from RFC 822
The following lexical tokens, defined in [6], are used in the ABNF
grammar for DSNs: atom, CHAR, comment, CR, CRLF, DIGIT, LF, linear-
white-space, SPACE, text. The date-time lexical token is defined in
[8].
Moore & Vaudreuil Standards Track [Page 10]
RFC 1894 Delivery Status Notifications January 1996
2.2 Per-Message DSN Fields
Some fields of a DSN apply to all of the delivery attempts described
by that DSN. These fields may appear at most once in any DSN. These
fields are used to correlate the DSN with the original message
transaction and to provide additional information which may be useful
to gateways.
per-message-fields =
[ original-envelope-id-field CRLF ]
reporting-mta-field CRLF
[ dsn-gateway-field CRLF ]
[ received-from-mta-field CRLF ]
[ arrival-date-field CRLF ]
*( extension-field CRLF )
2.2.1 The Original-Envelope-Id field
The optional Original-Envelope-Id field contains an "envelope
identifier" which uniquely identifies the transaction during which
the message was submitted, and was either (a) specified by the sender
and supplied to the sender's MTA, or (b) generated by the sender's
MTA and made available to the sender when the message was submitted.
Its purpose is to allow the sender (or her user agent) to associate
the returned DSN with the specific transaction in which the message
was sent.
If such an envelope identifier was present in the envelope which
accompanied the message when it arrived at the Reporting MTA, it
SHOULD be supplied in the Original-Envelope-Id field of any DSNs
issued as a result of an attempt to deliver the message. Except when
a DSN is issued by the sender's MTA, an MTA MUST NOT supply this
field unless there is an envelope-identifier field in the envelope
which accompanied this message on its arrival at the Reporting MTA.
The Original-Envelope-Id field is defined as follows:
original-envelope-id-field =
"Original-Envelope-Id" ":" envelope-id
envelope-id = *text
There may be at most one Original-Envelope-Id field per DSN.
The envelope-id is CASE-SENSITIVE. The DSN MUST preserve the
original case and spelling of the envelope-id.
Moore & Vaudreuil Standards Track [Page 11]
RFC 1894 Delivery Status Notifications January 1996
NOTE: The Original-Envelope-Id is NOT the same as the Message-Id from
the message header. The Message-Id identifies the content of the
message, while the Original-Envelope-Id identifies the transaction in
which the message is sent.
2.2.2 The Reporting-MTA DSN field
reporting-mta-field =
"Reporting-MTA" ":" mta-name-type ";" mta-name
mta-name = *text
The Reporting-MTA field is defined as follows:
A DSN describes the results of attempts to deliver, relay, or gateway
a message to one or more recipients. In all cases, the Reporting-MTA
is the MTA which attempted to perform the delivery, relay, or gateway
operation described in the DSN. This field is required.
Note that if an SMTP client attempts to relay a message to an SMTP
server and receives an error reply to a RCPT command, the client is
responsible for generating the DSN, and the client's domain name will
appear in the Reporting-MTA field. (The server's domain name will
appear in the Remote-MTA field.)
Note that the Reporting-MTA is not necessarily the MTA which actually
issued the DSN. For example, if an attempt to deliver a message
outside of the Internet resulted in a nondelivery notification which
was gatewayed back into Internet mail, the Reporting-MTA field of the
resulting DSN would be that of the MTA that originally reported the
delivery failure, not that of the gateway which converted the foreign
notification into a DSN. See Figure 2.
Moore & Vaudreuil Standards Track [Page 12]
RFC 1894 Delivery Status Notifications January 1996
sender's environment recipient's environment
............................ ..........................................
: :
(1) : : (2)
+-----+ +--------+ +--------+ +---------+ +---------+ +------+
| | | | | | |Received-| | | | |
| |=>|Original|=>| |->| From |->|Reporting|-->|Remote|
| user| | MTA | | | | MTA | | MTA |") (so that no DSNs would be sent from a downstream
MTA to the original sender),
(e) for messages forwarded to a confidential address, disabling delivery
notifications for the forwarded message (e.g. if the "next-hop" MTA
uses ESMTP and supports the DSN extension, by using the NOTIFY=NEVER
parameter to the RCPT command), or
(f) when forwarding mail to a confidential address, having the
forwarding MTA rewrite the envelope return address for the forwarded
message and attempt delivery of that message as if the forwarding
MTA were the originator. On its receipt of final delivery status,
the forwarding MTA would issue a DSN to the original sender.
In general, any optional DSN field may be omitted if the Reporting
MTA site determines that inclusion of the field would impose too
great a compromise of site confidentiality. The need for such
confidentiality must be balanced against the utility of the omitted
information in trouble reports and DSNs gatewayed to foreign
environments.
Implementors are cautioned that many existing MTAs will send
nondelivery notifications to a return address in the message header
(rather than to the one in the envelope), in violation of SMTP and
other protocols. If a message is forwarded through such an MTA, no
reasonable action on the part of the forwarding MTA will prevent the
downstream MTA from compromising the forwarding address. Likewise,
if the recipient's MTA automatically responds to messages based on a
request in the message header (such as the nonstandard, but widely
used, Return-Receipt-To extension header), it will also compromise
the forwarding address.
4.3 Non-Repudiation
Within the framework of today's internet mail, the DSNs defined in
this memo provide valuable information to the mail user; however,
even a "failed" DSN can not be relied upon as a guarantee that a
message was not received by the recipient. Even if DSNs are not
actively forged, conditions exist under which a message can be
delivered despite the fact that a failure DSN was issued.
Moore & Vaudreuil Standards Track [Page 24]
RFC 1894 Delivery Status Notifications January 1996
For example, a race condition in the SMTP protocol allows for the
duplication of messages if the connection is dropped following a
completed DATA command, but before a response is seen by the SMTP
client. This will cause the SMTP client to retransmit the message,
even though the SMTP server has already accepted it.[9] If one of
those delivery attempts succeeds and the other one fails, a "failed"
DSN could be issued even though the message actually reached the
recipient.
Moore & Vaudreuil Standards Track [Page 25]
RFC 1894 Delivery Status Notifications January 1996
5. Appendix - collected grammar
NOTE: The following lexical tokens are defined in RFC 822: atom,
CHAR, comment, CR, CRLF, DIGIT, LF, linear-white-space, SPACE, text.
The date-time lexical token is defined in [8].
action-field = "Action" ":" action-value
action-value =
"failed" / "delayed" / "delivered" / "relayed" / "expanded"
address-type = atom
arrival-date-field = "Arrival-Date" ":" date-time
delivery-status-content =
per-message-fields 1*( CRLF per-recipient-fields )
diagnostic-code-field =
"Diagnostic-Code" ":" diagnostic-type ";" *text
diagnostic-type = atom
dsn-gateway-field = "DSN-Gateway" ":" mta-name-type ";" mta-name
envelope-id = *text
extension-field = extension-field-name ":" *text
extension-field-name = atom
final-recipient-field =
"Final-Recipient" ":" address-type ";" generic-address
generic-address = *text
last-attempt-date-field = "Last-Attempt-Date" ":" date-time
mta-name = *text
mta-name-type = atom
original-envelope-id-field =
"Original-Envelope-Id" ":" envelope-id
original-recipient-field =
"Original-Recipient" ":" address-type ";" generic-address
Moore & Vaudreuil Standards Track [Page 26]
RFC 1894 Delivery Status Notifications January 1996
per-message-fields =
[ original-envelope-id-field CRLF ]
reporting-mta-field CRLF
[ dsn-gateway-field CRLF ]
[ received-from-mta-field CRLF ]
[ arrival-date-field CRLF ]
*( extension-field CRLF )
per-recipient-fields =
[ original-recipient-field CRLF ]
final-recipient-field CRLF
action-field CRLF
status-field CRLF
[ remote-mta-field CRLF ]
[ diagnostic-code-field CRLF ]
[ last-attempt-date-field CRLF ]
[ will-retry-until-field CRLF ]
*( extension-field CRLF )
received-from-mta-field =
"Received-From-MTA" ":" mta-name-type ";" mta-name
remote-mta-field = "Remote-MTA" ":" mta-name-type ";" mta-name
reporting-mta-field =
"Reporting-MTA" ":" mta-name-type ";" mta-name
status-code = DIGIT "." 1*3DIGIT "." 1*3DIGIT
; White-space characters and comments are NOT allowed within a
; status-code, though a comment enclosed in parentheses MAY follow
; the last numeric subfield of the status-code. Each numeric
; subfield within the status-code MUST be expressed without
; leading zero digits.
status-field = "Status" ":" status-code
will-retry-until-field = "Will-Retry-Until" ":" date-time
Moore & Vaudreuil Standards Track [Page 27]
RFC 1894 Delivery Status Notifications January 1996
6. Appendix - Guidelines for gatewaying DSNs
NOTE: This section provides non-binding recommendations for the
construction of mail gateways that wish to provide semi-transparent
delivery reports between the Internet and another electronic mail
system. Specific DSN gateway requirements for a particular pair of
mail systems may be defined by other documents.
6.1 Gatewaying from other mail systems to DSNs
A mail gateway may issue a DSN to convey the contents of a "foreign"
delivery or non-delivery notification over Internet mail. When there
are appropriate mappings from the foreign notification elements to
DSN fields, the information may be transmitted in those DSN fields.
Additional information (such as might be useful in a trouble ticket
or needed to tunnel the foreign notification through the Internet)
may be defined in extension DSN fields. (Such fields should be given
names that identify the foreign mail protocol, e.g. X400-* for X.400
NDN or DN protocol elements)
The gateway must attempt to supply reasonable values for the
Reporting-MTA, Final-Recipient, Action, and Status fields. These
will normally be obtained by translating the values from the remote
delivery or non-delivery notification into their Internet-style
equivalents. However, some loss of information is to be expected.
For example, the set of status-codes defined for DSNs may not be
adequate to fully convey the delivery diagnostic code from the
foreign system. The gateway should assign the most precise code
which describes the failure condition, falling back on "generic"
codes such as 2.0.0 (success), 4.0.0 (temporary failure), and 5.0.0
(permanent failure) when necessary. The actual foreign diagnostic
code should be retained in the Diagnostic-Code field (with an
appropriate diagnostic-type value) for use in trouble tickets or
tunneling.
The sender-specified recipient address, and the original envelope-id,
if present in the foreign transport envelope, should be preserved in
the Original-Recipient and Original-Envelope-ID fields.
The gateway should also attempt to preserve the "final" recipient
addresses and MTA names from the foreign system. Whenever possible,
foreign protocol elements should be encoded as meaningful printable
ASCII strings.
For DSNs produced from foreign delivery or nondelivery notifications,
the name of the gateway MUST appear in the DSN-Gateway field of the
DSN.
Moore & Vaudreuil Standards Track [Page 28]
RFC 1894 Delivery Status Notifications January 1996
6.2 Gatewaying from DSNs to other mail systems
It may be possible to gateway DSNs from the Internet into a foreign
mail system. The primary purpose of such gatewaying is to convey
delivery status information in a form that is usable by the
destination system. A secondary purpose is to allow "tunneling" of
DSNs through foreign mail systems, in case the DSN may be gatewayed
back into the Internet.
In general, the recipient of the DSN (i.e., the sender of the
original message) will want to know, for each recipient: the closest
available approximation to the original recipient address, the
delivery status (success, failure, or temporary failure), and for
failed deliveries, a diagnostic code that describes the reason for
the failure.
If possible, the gateway should attempt to preserve the Original-
Recipient address and Original-Envelope-ID (if present), in the
resulting foreign delivery status report.
When reporting delivery failures, if the diagnostic-type subfield of
the Diagnostic-Code field indicates that the original diagnostic code
is understood by the destination environment, the information from
the Diagnostic-Code field should be used. Failing that, the
information in the Status field should be mapped into the closest
available diagnostic code used in the destination environment.
If it is possible to tunnel a DSN through the destination
environment, the gateway specification may define a means of
preserving the DSN information in the delivery status reports used by
that environment.
Moore & Vaudreuil Standards Track [Page 29]
RFC 1894 Delivery Status Notifications January 1996
7. Appendix - Guidelines for use of DSNs by mailing list exploders
NOTE: This section pertains only to the use of DSNs by "mailing
lists" as defined in [4], section 7.2.7.
DSNs are designed to be used by mailing list exploders to allow them
to detect and automatically delete recipients for whom mail delivery
fails repeatedly.
When forwarding a message to list subscribers, the mailing list
exploder should always set the envelope return address (e.g. SMTP
MAIL FROM address) to point to a special address which is set up to
received nondelivery reports. A "smart" mailing list exploder can
therefore intercept such nondelivery reports, and if they are in the
DSN format, automatically examine them to determine for which
recipients a message delivery failed or was delayed.
The Original-Recipient field should be used if available, since it
should exactly match the subscriber address known to the list. If
the Original-Recipient field is not available, the recipient field
may resemble the list subscriber address. Often, however, the list
subscriber will have forwarded his mail to a different address, or
the address may be subject to some re-writing, so heuristics may be
required to successfully match an address from the recipient field.
Care is needed in this case to minimize the possibility of false
matches.
The reason for delivery failure can be obtained from the Status and
Action fields, and from the Diagnostic-Code field (if the status-type
is recognized). Reports for recipients with action values other than
"failed" can generally be ignored; in particular, subscribers should
not be removed from a list due to "delayed" reports.
In general, almost any failure status code (even a "permanent" one)
can result from a temporary condition. It is therefore recommended
that a list exploder not delete a subscriber based on any single
failure DSN (regardless of the status code), but only on the
persistence of delivery failure over a period of time.
However, some kinds of failures are less likely than others to have
been caused by temporary conditions, and some kinds of failures are
more likely to be noticed and corrected quickly than others. Once
more precise status codes are defined, it may be useful to
differentiate between the status codes when deciding whether to
delete a subscriber. For example, on a list with a high message
volume, it might be desirable to temporarily suspend delivery to a
recipient address which causes repeated "temporary" failures, rather
than simply deleting the recipient. The duration of the suspension
Moore & Vaudreuil Standards Track [Page 30]
RFC 1894 Delivery Status Notifications January 1996
might depend on the type of error. On the other hand, a "user
unknown" error which persisted for several days could be considered a
reliable indication that address were no longer valid.
8. Appendix - IANA registration forms for DSN types
The forms below are for use when registering a new address-type,
diagnostic-type, or MTA-name-type with the Internet Assigned Numbers
Authority (IANA). Each piece of information requested by a
registration form may be satisfied either by providing the
information on the form itself, or by including a reference to a
published, publicly available specification which includes the
necessary information. IANA MAY reject DSN type registrations
because of incomplete registration forms, imprecise specifications,
or inappropriate type names.
To register a DSN type, complete the applicable form below and send
it via Internet electronic mail to .
8.1 IANA registration form for address-type
A registration for a DSN address-type MUST include the following
information:
(a) The proposed address-type name.
(b) The syntax for mailbox addresses of this type, specified using BNF,
regular expressions, ASN.1, or other non-ambiguous language.
(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.
(d) [optional] A specification for how addresses of this type are to be
translated to and from Internet electronic mail addresses.
8.2 IANA registration form for diagnostic-type
A registration for a DSN address-type MUST include the following
information:
(a) The proposed diagnostic-type name.
(b) A description of the syntax to be used for expressing diagnostic
codes of this type as graphic characters from the US-ASCII
repertoire.
Moore & Vaudreuil Standards Track [Page 31]
RFC 1894 Delivery Status Notifications January 1996
(c) A list of valid diagnostic codes of this type and the meaning of
each code.
(d) [optional] A specification for mapping from diagnostic codes of this
type to DSN status codes (as defined in [5]).
8.3 IANA registration form for MTA-name-type
A registration for a DSN MTA-name-type must include the following
information:
(a) The proposed MTA-name-type name.
(b) A description of the syntax of MTA names of this type, using BNF,
regular expressions, ASN.1, or other non-ambiguous language.
(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.
Moore & Vaudreuil Standards Track [Page 32]
RFC 1894 Delivery Status Notifications January 1996
9. Appendix - Examples
NOTE: These examples are provided as illustration only, and are not
considered part of the DSN protocol specification. If an example
conflicts with the protocol definition above, the example is wrong.
Likewise, the use of *-type subfield names or extension fields in
these examples is not to be construed as a definition for those type
names or extension fields.
These examples were manually translated from bounced messages using
whatever information was available.
Moore & Vaudreuil Standards Track [Page 33]
RFC 1894 Delivery Status Notifications January 1996
9.1 This is a simple DSN issued after repeated attempts
to deliver a message failed. In this case, the DSN is
issued by the same MTA from which the message was originated.
Date: Thu, 7 Jul 1994 17:16:05 -0400
From: Mail Delivery Subsystem
Message-Id: <199407072116.RAA14128@CS.UTK.EDU>
Subject: Returned mail: Cannot send message for 5 days
To:
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary="RAA14128.773615765/CS.UTK.EDU"
--RAA14128.773615765/CS.UTK.EDU
The original message was received at Sat, 2 Jul 1994 17:10:28 -0400
from root@localhost
----- The following addresses had delivery problems -----
(unrecoverable error)
----- Transcript of session follows -----
... Deferred: Connection timed out
with larry.slip.umd.edu.
Message could not be delivered for 5 days
Message will be deleted from queue
--RAA14128.773615765/CS.UTK.EDU
content-type: message/delivery-status
Reporting-MTA: dns; cs.utk.edu
Original-Recipient: rfc822;louisl@larry.slip.umd.edu
Final-Recipient: rfc822;louisl@larry.slip.umd.edu
Action: failed
Status: 4.0.0
Diagnostic-Code: smtp; 426 connection timed out
Last-Attempt-Date: Thu, 7 Jul 1994 17:15:49 -0400
--RAA14128.773615765/CS.UTK.EDU
content-type: message/rfc822
[original message goes here]
--RAA14128.773615765/CS.UTK.EDU--
Moore & Vaudreuil Standards Track [Page 34]
RFC 1894 Delivery Status Notifications January 1996
9.2 This is another DSN issued by the sender's MTA, which
contains details of multiple delivery attempts. Some of
these were detected locally, and others by a remote MTA.
Date: Fri, 8 Jul 1994 09:21:47 -0400
From: Mail Delivery Subsystem
Subject: Returned mail: User unknown
To:
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary="JAA13167.773673707/CS.UTK.EDU"
--JAA13167.773673707/CS.UTK.EDU
content-type: text/plain; charset=us-ascii
----- The following addresses had delivery problems -----
(unrecoverable error)
(unrecoverable error)
--JAA13167.773673707/CS.UTK.EDU
content-type: message/delivery-status
Reporting-MTA: dns; cs.utk.edu
Original-Recipient: rfc822;arathib@vnet.ibm.com
Final-Recipient: rfc822;arathib@vnet.ibm.com
Action: failed
Status: 5.0.0 (permanent failure)
Diagnostic-Code: smtp;
550 'arathib@vnet.IBM.COM' is not a registered gateway user
Remote-MTA: dns; vnet.ibm.com
Original-Recipient: rfc822;johnh@hpnjld.njd.hp.com
Final-Recipient: rfc822;johnh@hpnjld.njd.hp.com
Action: delayed
Status: 4.0.0 (hpnjld.njd.jp.com: host name lookup failure)
Original-Recipient: rfc822;wsnell@sdcc13.ucsd.edu
Final-Recipient: rfc822;wsnell@sdcc13.ucsd.edu
Action: failed
Status: 5.0.0
Diagnostic-Code: smtp; 550 user unknown
Remote-MTA: dns; sdcc13.ucsd.edu
--JAA13167.773673707/CS.UTK.EDU
content-type: message/rfc822
Moore & Vaudreuil Standards Track [Page 35]
RFC 1894 Delivery Status Notifications January 1996
[original message goes here]
--JAA13167.773673707/CS.UTK.EDU--
9.3 A delivery report generated by Message Router (MAILBUS) and
gatewayed by PMDF_MR to a DSN. In this case the gateway did not
have sufficient information to supply an original-recipient address.
Disclose-recipients: prohibited
Date: Fri, 08 Jul 1994 09:21:25 -0400 (EDT)
From: Message Router Submission Agent
Subject: Status of : Re: Battery current sense
To: owner-ups-mib@CS.UTK.EDU
Message-id: <01HEGJ0WNBY28Y95LN@mr.timeplex.com>
MIME-version: 1.0
content-type: multipart/report; report-type=delivery-status;
boundary="84229080704991.122306.SYS30"
--84229080704991.122306.SYS30
content-type: text/plain
Invalid address - nair_s
%DIR-E-NODIRMTCH, No matching Directory Entry found
--84229080704991.122306.SYS30
content-type: message/delivery-status
Reporting-MTA: mailbus; SYS30
Final-Recipient: unknown; nair_s
Status: 5.0.0 (unknown permanent failure)
Action: failed
--84229080704991.122306.SYS30--
Moore & Vaudreuil Standards Track [Page 36]
RFC 1894 Delivery Status Notifications January 1996
9.4 A delay report from a multiprotocol MTA. Note that there is no
returned content, so no third body part appears in the DSN.
From:
Message-Id: <199407092338.TAA23293@CS.UTK.EDU>
Received: from nsfnet-relay.ac.uk by sun2.nsfnet-relay.ac.uk
id ;
Sun, 10 Jul 1994 00:36:51 +0100
To: owner-info-mime@cs.utk.edu
Date: Sun, 10 Jul 1994 00:36:51 +0100
Subject: WARNING: message delayed at "nsfnet-relay.ac.uk"
content-type: multipart/report; report-type=delivery-status;
boundary=foobar
--foobar
content-type: text/plain
The following message:
UA-ID: Reliable PC (...
Q-ID: sun2.nsf:77/msg.11820-0
has not been delivered to the intended recipient:
thomas@de-montfort.ac.uk
despite repeated delivery attempts over the past 24 hours.
The usual cause of this problem is that the remote system is
temporarily unavailable.
Delivery will continue to be attempted up to a total elapsed
time of 168 hours, ie 7 days.
You will be informed if delivery proves to be impossible
within this time.
Please quote the Q-ID in any queries regarding this mail.
--foobar
content-type: message/delivery-status
Reporting-MTA: dns; sun2.nsfnet-relay.ac.uk
Final-Recipient: rfc822;thomas@de-montfort.ac.uk
Status: 4.0.0 (unknown temporary failure)
Action: delayed
Moore & Vaudreuil Standards Track [Page 37]
RFC 1894 Delivery Status Notifications January 1996
--foobar--
10. Acknowledgments
The authors wish to thank the following people for their reviews of
earlier drafts of this document and their suggestions for
improvement: Eric Allman, Harald Alvestrand, Allan Cargille, Jim
Conklin, Peter Cowen, Dave Crocker, Roger Fajman, Ned Freed, Marko
Kaittola, Steve Kille, John Klensin, John Gardiner Myers, Mark
Nahabedian, Julian Onions, Jacob Palme, Jean Charles Roy, and Gregory
Sheehan.
11. References
[1] Borenstein, N., Freed, N. "Multipurpose Internet Mail Extensions",
RFC 1521, Bellcore, Innosoft, September 1993.
[2] Vaudreuil, G., "The Multipart/Report Content Type for the Reporting
of Mail System Administrative Messages", RFC 1892, Octal Network
Services, January 1996.
[3] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
USC/Information Sciences Institute, August 1982.
[4] Moore, K., "SMTP Service Extension for Delivery Status
Notifications", RFC 1891, University of Tennessee, January 1996.
[5] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 1893, Octal
Network Services, January 1996.
[6] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, UDEL, August 1982.
[7] Moore, K. "MIME (Multipurpose Internet Mail Extensions) Part Two:
Message Header Extensions for Non-Ascii Text", RFC 1522, University
of Tennessee, September 1993.
[8] Braden, R. (ed.) "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, USC/Information Sciences Institute,
October 1989.
[9] Partridge, C., "Duplicate Messages and SMTP", RFC 1047, BBN,
February 1988.
Moore & Vaudreuil Standards Track [Page 38]
RFC 1894 Delivery Status Notifications January 1996
11. Authors' Addresses
Keith Moore
University of Tennessee
107 Ayres Hall
Knoxville, TN 37996-1301
USA
EMail: moore@cs.utk.edu
Phone: +1 615 974 3126
Fax: +1 615 974 8296
Gregory M. Vaudreuil
Octel Network Services
17080 Dallas Parkway
Dallas, TX 75248-1905
USA
EMail: Greg.Vaudreuil@Octel.Com
Moore & Vaudreuil Standards Track [Page 39]
RFC, FYI, BCP