< draft-vaudreuil-1894bis-01.txt		draft-vaudreuil-1894bis-02.txt >
			A new Request for Comments is now available in online RFC libraries.
	Internet Draft Keith Moore		RFC 3464
	Expires in six months University of Tennessee
	Greg Vaudreuil
	Lucent Technologies
	April 16, 2002
	An Extensible Message Format for Delivery Status Notifications
	<draft-vaudreuil-1894bis-01.txt>
	Status of this Memo
	This document is an Internet-Draft and is in full conformance with all
	provisions of Section 10 of RFC 2026.
	This document is an Internet Draft. Internet Drafts are working documents
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	Copyright Notice
	Copyright (C) The Internet Society (2002). All Rights Reserved.
	This Internet-Draft is in conformance with Section 10 of RFC 2026.
	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.
	Working Group Summary
	RFC 1894 was a product of the Notary working group. This document is a
	revision of that document providing clarifications as necessary to
	advance to draft standard.
	Any questions, comments, and reports of defects or ambiguities in this
	specification may be sent to the mailing list for the NOTARY working
	group of the IETF, using the address <notifications@cs.utk.edu>. Requests
	to subscribe to the mailing list should be addressed to <notifications-
	request@cs.utk.edu>. Implementers 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.
	Document Conventions
	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 RFC-2119 [RFC2119].
	Table of Contents
	1. INTRODUCTION ........................................................4
	1.1 Purposes .........................................................4
	1.2 Requirements .....................................................5
	1.3 Terminology ......................................................5
	2. FORMAT OF A DELIVERY STATUS NOTIFICATION ............................8
	2.1 The message/delivery-status content-type .........................9
	2.1.1 General conventions for DSN fields ............................9
	2.1.2 "*-type" sub-fields ...........................................9
	2.1.3 Lexical tokens imported from RFC 822 .........................10
	2.2 Per-Message DSN Fields ..........................................10
	2.2.1 The Original-Envelope-Id field ...............................11
	2.2.2 The Reporting-MTA DSN field ..................................11
	2.2.3 The DSN-Gateway field ........................................12
	2.2.4 The Received-From-MTA DSN field ..............................13
	2.2.5 The Arrival-Date DSN field ...................................13
	2.3 Per-Recipient DSN fields ........................................13
	2.3.1 Original-Recipient field .....................................14
	2.3.2 Final-Recipient field ........................................14
	2.3.3 Action field .................................................15
	2.3.4 Status field .................................................16
	2.3.5 Remote-MTA field .............................................17
	2.3.6 Diagnostic-Code field ........................................17
	2.3.7 Last-Attempt-Date field ......................................18
	2.3.8 final-log-id field ...........................................18
	2.3.9 Will-Retry-Until field .......................................18
	3. CONFORMANCE AND USAGE REQUIREMENTS .................................20
	4. SECURITY CONSIDERATIONS ............................................21
	4.1 Forgery .........................................................21
	4.2 Confidentiality .................................................21
	4.3 Non-Repudiation .................................................22
	5. REFERENCES .........................................................23
	7. ACKNOWLEDGMENTS ....................................................25
	8. AUTHOR'S ADDRESS ...................................................25
	APPENDIX A - COLLECTED GRAMMAR ........................................26
	APPENDIX B - GUIDELINES FOR GATEWAYING DSNS ...........................28
	Gatewaying from other mail systems to DSNs ..........................28
	Gatewaying from DSNs to other mail systems ..........................28
	APPENDIX C - GUIDELINES FOR USE OF DSNS BY MAILING LIST EXPLODERS .....30
	APPENDIX D - IANA REGISTRATION FORMS FOR DSN TYPES ....................31
	IANA registration form for address-type .............................31
	IANA registration form for diagnostic-type ..........................31
	IANA registration form for MTA-name-type ............................31
	APPENDIX E - EXAMPLES .................................................33
	Simple DSN ..........................................................34
	Multi-Recipient DSN .................................................35
	DSN from gateway to foreign system ..................................36
	Delayed DSN .........................................................37
	APPENDIX F - CHANGES FROM RFC1894 .....................................38
	1. Introduction
	This memo defines a MIME [MIME1] 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 [REPORT].
	This memo defines only the format of the notifications. An extension to
	the Simple Message Transfer Protocol (SMTP)[SMTP] to fully support such
	notifications is the subject of a separate memo [DRPT].
	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 that is largely independent of human language and media;
	(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 and medium-independent, yet reasonably
	precise, indications of the reason for the failure of a message to be
	delivered; 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 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 that 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.
	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.
	Figure 1 illustrates the relationship between the various MTAs.
	+-----+ +--------+ +---------+ +---------+ +------+
	| | | | |Received-| | | | |
	| | => |Original| => ... => | From | => |Reporting| ===> |Remote|
	| user| | MTA | | MTA | | MTA | <No! | MTA |
	|agent| +--------+ +---------+ +----v----+ +------+
	| | |
	| | <-------------------------------------------+
	+-----+ (DSN returned to sender by Reporting MTA)
	Figure 1. Original, Received-From, Reporting and Remote MTAs
	Each of these MTAs may provide information that is useful in a DSN:
	+ Ideally, the DSN will contain the address of each recipient as
	originally specified to the Original MTA by the sender of the message.
	This version of the address is needed (rather than a forwarding address
	or some modified version of the original address) so that the sender
	may compare the recipient address in the DSN with the address in the
	sender's records (e.g. an address book for an individual, the list of
	subscribers for a mailing list) and take appropriate action.
	Similarly, the DSN might contain an "envelope identifier" that was
	known to both the sender's user agent and the Original MTA at the time
	of message submission, and which, if included in the DSN, can be used
	by the sender to keep track of which messages were or were not
	delivered.
	+ If a message was (a) forwarded to a different address than that
	specified by the sender, (b) gatewayed to a different mail system than
	that used by the sender, or (c) subjected to address rewriting during
	transmission, the "final" form of the recipient address (i.e. the one
	seen by the Reporting MTA) will be different than the original (sender-
	specified) recipient address. Just as the sender's user agent (or the
	sender) prefers the original recipient address, so the "final" address
	is needed when reporting a problem to the postmaster of the site where
	message delivery failed, because only the final recipient address will
	allow her to reproduce the conditions that caused the failure.
	+ A "failed" DSN should contain the most accurate explanation for the
	delivery failure that is available. For ease of interpretation, this
	information should be a format that is independent of the mail
	transport system that issued the DSN. However, if a foreign error code
	is translated into some transport-independent format, some information
	may be lost. It is therefore desirable to provide both a transport-
	independent status code and a mechanism for reporting transport-
	specific codes. Depending on the circumstances that produced delivery
	failure, the transport-specific code might be obtained from either the
	Reporting MTA or the Remote MTA.
	Since different values for "recipient address" and "delivery status code"
	are needed according to the circumstance in which a DSN will be used, and
	since the MTA that issues the DSN cannot anticipate those circumstances,
	the DSN format described here may contain both the original and final
	forms of a recipient address, and both a transport-independent and a
	transport-specific indication of delivery status.
	Extension fields may also be added by the Reporting MTA as needed to
	provide additional information for use in a trouble ticket or to preserve
	information for tunneling of foreign delivery reports through Internet
	DSNs.
	The Original, Reporting, and Remote MTAs may exist in very different
	environments and use dissimilar transport protocols, MTA names, address
	formats, and delivery status codes. DSNs therefore do not assume any
	particular format for mailbox addresses, MTA names, or transport-specific
	status codes. Instead, the various DSN fields that carry such quantities
	consist of a "type" sub-field followed by a sub-field whose contents are
	ordinary text characters, and the format of which is indicated by the
	"type" sub-field. This allows a DSN to convey these quantities regardless
	of format.
	2. Format of a Delivery Status Notification
	A DSN is a MIME message with a top-level content-type of multipart/report
	(defined in [REPORT]). When a multipart/report content is used to
	transmit a DSN:
	(a) The report-type parameter of the multipart/report content is
	"delivery-status".
	(b) The first component of the multipart/report contains a human-
	readable explanation of the DSN, as described in [REPORT].
	(c) The second component of the multipart/report is of content-type
	message/delivery-status, described in section 2.1 of this document.
	(d) If the original message or a portion of the message is to be returned
	to the sender, it appears as the third component of the
	multipart/report.
	NOTE: For delivery status notifications gatewayed from foreign systems,
	the headers of the original message may not be available. In this case
	the third component of the DSN may be omitted, or it may contain
	"simulated" RFC 822 headers that contain equivalent information. In
	particular, it is very desirable to preserve the subject, date, and
	message-id (or equivalent) fields from the original message.
	The DSN MUST be addressed (in both the message header and the transport
	envelope) to the return address from the transport envelope which
	accompanied the original message for which the DSN was generated. (For a
	message that arrived via SMTP, the envelope return address appears in the
	MAIL FROM command.)
	The From field of the message header of the DSN SHOULD contain the
	address of a human who is responsible for maintaining the mail system at
	the Reporting MTA site (e.g. Postmaster), so that a reply to the DSN will
	reach that person. Exception: if a DSN is translated from a foreign
	delivery report, and the gateway performing the translation cannot
	determine the appropriate address, the From field of the DSN MAY be the
	address of a human who is responsible for maintaining the gateway.
	The envelope sender address of the DSN SHOULD be chosen to ensure that no
	delivery status reports will be issued in response to the DSN itself, and
	MUST be chosen so that DSNs will not generate mail loops. Whenever an
	SMTP transaction is used to send a DSN, the MAIL FROM command MUST use a
	NULL return address, i.e. "MAIL FROM:<>".
	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.
	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
	[RFC822]). 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 that 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 [MIME3].
	2.1.2 "*-type" sub-fields
	Several DSN fields consist of a "-type" sub-field, followed by a
	semicolon, followed by "*text". For these fields, the keyword used in the
	address-type, diagnostic-type, or MTA-name-type sub-field indicates the
	expected format of the address, status-code, or MTA- name which follows.
	The "-type" sub-fields 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 [SMTP], 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 one or more specifications that provide such descriptions.
	(The "rfc822" address-type, "smtp" diagnostic- type, and "dns" MTA-name-
	type are defined in [DRPT].) Registration forms for address-type,
	diagnostic-type, and MTA-name-type appear in Appendix D.
	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 [RFC822], 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
	[HOSTREQ].
	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"
	that 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 that
	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 that 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.
	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 that 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 non-delivery 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.
	sender's environment recipient's environment
	............................ ..........................................
	: :
	(1) : : (2)
	+-----+ +--------+ +--------+ +---------+ +---------+ +------+
	| | | | | | |Received-| | | | |
	| |=>|Original|=>| |->| From |->|Reporting|-->|Remote|
	| user| | MTA | | | | MTA | | MTA |<No| MTA |
	|agent| +--------+ |Gateway | +---------+ +----v----+ +------+
	| | | | |
	| | <============| |<-------------------+
	+-----+ | |(4) (3)
	+--------+
	: :
	...........................: :.........................................
	Figure 2. DSNs in the presence of gateways
	(1) message is gatewayed into recipient's environment
	(2) attempt to relay message fails
	(3) reporting-mta (in recipient's environment) returns non-delivery
	notification
	(4) gateway translates foreign notification into a DSN
	The mta-name portion of the Reporting-MTA field is formatted according to
	the conventions indicated by the mta-name-type sub-field. If an MTA
	functions as a gateway between dissimilar mail environments and thus is
	known by multiple names depending on the environment, the mta-name sub-
	field SHOULD contain the name used by the environment from which the
	message was accepted by the Reporting-MTA.
	Because the exact spelling of an MTA name may be significant in a
	particular environment, MTA names are CASE-SENSITIVE.
	2.2.3 The DSN-Gateway field
	The DSN-Gateway field indicates the name of the gateway or MTA that
	translated a foreign (non-Internet) delivery status notification into
	this DSN. This field MUST appear in any DSN that was translated by a
	gateway from a foreign system into DSN format, and MUST NOT appear
	otherwise.
	dsn-gateway field = "DSN
	For gateways into Internet mail, the MTA-name-type will normally be
	"dns", and the mta-name will be the Internet domain name of the gateway.
	2.2.4 The Received-From-MTA DSN field
	The optional Received-From-MTA field indicates the name of the MTA from
	which the message was received.
	received-from-mta-field =
	"Received-From-MTA" ":" mta-name-type ";" mta-name
	If the message was received from an Internet host via SMTP, the contents
	of the mta-name sub-field SHOULD be the Internet domain name supplied in
	the HELO or EHLO command, and the network address used by the SMTP client
	SHOULD be included as a comment enclosed in parentheses. (In this case,
	the MTA-name-type will be "dns".)
	The mta-name portion of the Received-From-MTA field is formatted
	according to the conventions indicated by the MTA-name-type sub-field.
	Since case is significant in some mail systems, the exact spelling,
	including case, of the MTA name SHOULD be preserved.
	2.2.5 The Arrival-Date DSN field
	The optional Arrival-Date field indicates the date and time at which the
	message arrived at the Reporting MTA. If the Last-Attempt-Date field is
	also provided in a per-recipient field, this can be used to determine the
	interval between when the message arrived at the Reporting MTA and when
	the report was issued for that recipient.
	arrival-date-field = "Arrival-Date" ":" date-time
	The date and time are expressed in RFC 822 'date-time' format, as
	modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
	2.3 Per-Recipient DSN fields
	A DSN contains information about attempts to deliver a message to one or
	more recipients. The delivery information for any particular recipient is
	contained in a group of contiguous per-recipient fields. Each group of
	per-recipient fields is preceded by a blank line.
	The syntax for the group of per-recipient fields is as follows:
	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 ]
	[ final-log-id CRLF ]
	[ will-retry-until-field CRLF ]
	*( extension-field CRLF )
	2.3.1 Original-Recipient field
	The Original-Recipient field indicates the original recipient address as
	specified by the sender of the message for which the DSN is being issued.
	original-recipient-field =
	"Original-Recipient" ":" address-type ";" generic-address
	generic-address = *text
	The address-type field indicates the type of the original recipient
	address. If the message originated within the Internet, the address-type
	field will normally be "rfc822", and the address will be according to the
	syntax specified in [RFC822]. The value "unknown" should be used if the
	Reporting MTA cannot determine the type of the original recipient address
	from the message envelope.
	This field is optional. It should be included only if the sender-
	specified recipient address was present in the message envelope, such as
	by the SMTP extensions defined in [DRPT]. This address is the same as
	that provided by the sender and can be used to automatically correlate
	DSN reports and message transactions.
	2.3.2 Final-Recipient field
	The Final-Recipient field indicates the recipient for which this set of
	per-recipient fields applies. This field MUST be present in each set of
	per-recipient data.
	The syntax of the field is as follows:
	final-recipient-field =
	"Final-Recipient" ":" address-type ";" generic-address
	The generic-address sub-field of the Final-Recipient field MUST contain
	the mailbox address of the recipient (from the transport envelope), as it
	was when the Reporting MTA accepted the message for delivery.
	The Final-Recipient address may differ from the address originally
	provided by the sender, because it may have been transformed during
	forwarding and gatewaying into an totally unrecognizable mess. However,
	in the absence of the optional Original-Recipient field, the Final-
	Recipient field and any returned content may be the only information
	available with which to correlate the DSN with a particular message
	submission.
	The address-type sub-field indicates the type of address expected by the
	reporting MTA in that context. Recipient addresses obtained via SMTP will
	normally be of address-type "rfc822".
	NOTE: The Reporting MTA is not expected to ensure that the address
	actually conforms to the syntax conventions of the address-type. Instead,
	it MUST report exactly the address received in the envelope, unless that
	address contains characters such as CR or LF which are not allowed in a
	DSN field.
	Since mailbox addresses (including those used in the Internet) may be
	case sensitive, the case of alphabetic characters in the address MUST be
	preserved.
	2.3.3 Action field
	The Action field indicates the action performed by the Reporting-MTA as a
	result of its attempt to deliver the message to this recipient address.
	This field MUST be present for each recipient named in the DSN.
	The syntax for the action-field is:
	action-field = "Action" ":" action-value
	action-value =
	"failed" / "delayed" / "delivered" / "relayed" / "expanded"
	The action-value may be spelled in any combination of upper and lower
	case characters.
	"failed" indicates that the message could not be delivered to the
	recipient. The Reporting MTA has abandoned any attempts to
	deliver the message to this recipient. No further
	notifications should be expected.
	"delayed" indicates that the Reporting MTA has so far been unable to
	deliver or relay the message, but it will continue to
	attempt to do so. Additional notification messages may be
	issued as the message is further delayed or successfully
	delivered, or if delivery attempts are later abandoned.
	"delivered" indicates that the message was successfully delivered to
	the recipient address specified by the sender, which
	includes "delivery" to a mailing list exploder. It does
	not indicate that the message has been read. This is a
	terminal state and no further DSN for this recipient should
	be expected.
	"relayed" indicates that the message has been relayed or gatewayed
	into an environment that does not accept responsibility for
	generating DSNs upon successful delivery. This action-
	value SHOULD NOT be used unless the sender has requested
	notification of successful delivery for this recipient.
	"expanded" indicates that the message has been successfully delivered
	to the recipient address as specified by the sender, and
	forwarded by the Reporting-MTA beyond that destination to
	multiple additional recipient addresses. An action-value
	of "expanded" differs from "delivered" in that "expanded"
	is not a terminal state. Further "failed" and/or "delayed"
	notifications may be provided.
	Using the terms "mailing list" and "alias" as defined in [DRPT],
	section 7.2.7: An action-value of "expanded" is only to be used when
	the message is delivered to a multiple- recipient "alias". An
	action-value of "expanded" SHOULD NOT be used with a DSN issued on
	delivery of a message to a "mailing list".
	NOTE ON ACTION VS. STATUS CODES: Although the 'action' field
	might seem to be redundant with the 'status' field, this is not
	the case. In particular, a "temporary failure" ("4") status code
	could be used with an action-value of either "delayed" or
	"failed". For example, assume that an SMTP client repeatedly
	tries to relay a message to the mail exchanger for a recipient,
	but fails because a query to a domain name server timed out.
	After a few hours, it might issue a "delayed" DSN to inform the
	sender that the message had not yet been delivered. After a few
	days, the MTA might abandon its attempt to deliver the message
	and return a "failed" DSN. The status code (which would begin
	with a "4" to indicate "temporary failure") would be the same for
	both DSNs.
	Another example for which the action and status codes may appear
	contradictory: If an MTA or mail gateway cannot deliver a message
	because doing so would entail conversions resulting in an
	unacceptable loss of information, it would issue a DSN with the
	'action' field of "failure" and a status code of 'XXX'. If the
	message had instead been relayed, but with some loss of
	information, it might generate a DSN with the same XXX status-
	code, but with an action field of "relayed".
	2.3.4 Status field
	The per-recipient Status field contains a transport-independent status
	code that indicates the delivery status of the message to that recipient.
	This field MUST be present for each delivery attempt which is described
	by a DSN.
	The syntax of the status field is:
	status-field = "Status" ":" status-code
	status-code = 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 sub-field of the status-code. Each
	; numeric sub-field within the status-code MUST be expressed
	; without leading zero digits.
	Status codes thus consist of three numerical fields separated by ".". The
	first sub-field indicates whether the delivery attempt was successful (2
	= success, 4 = persistent temporary failure, 5 = permanent failure). The
	second sub-field indicates the probable source of any delivery anomalies,
	and the third sub-field denotes a precise error condition, if known.
	The initial set of status-codes is defined in [STATUS].
	2.3.5 Remote-MTA field
	The value associated with the Remote-MTA DSN field is a printable ASCII
	representation of the name of the "remote" MTA that reported delivery
	status to the "reporting" MTA.
	remote-mta field = "Remote
	NOTE: The Remote-MTA field preserves the "while talking to" information
	that was provided in some pre-existing nondelivery reports.
	This field is optional. It MUST NOT be included if no remote MTA was
	involved in the attempted delivery of the message to that recipient.
	2.3.6 Diagnostic-Code field
	For a "failed" or "delayed" recipient, the Diagnostic-Code DSN field
	contains the actual diagnostic code issued by the mail transport. Since
	such codes vary from one mail transport to another, the diagnostic-type
	sub-field is needed to specify which type of diagnostic code is
	represented.
	diagnostic-code-field =
	"Diagnostic-Code" ":" diagnostic-type ";" *text
	NOTE: The information in the Diagnostic-Code field may be somewhat
	redundant with that from the Status field. The Status field is
	needed so that any DSN, regardless of origin, may be understood by
	any user agent or gateway that parses DSNs. Since the Status code
	will sometimes be less precise than the actual transport diagnostic
	code, the Diagnostic-Code field is provided to retain the latter
	information. Such information may be useful in a trouble ticket sent
	to the administrator of the Reporting MTA, or when tunneling foreign
	non-delivery reports through DSNs.
	If the Diagnostic Code was obtained from a Remote MTA during an attempt
	to relay the message to that MTA, the Remote-MTA field should be present.
	When interpreting a DSN, the presence of a Remote-MTA field indicates
	that the Diagnostic Code was issued by the Remote MTA. The absence of a
	Remote-MTA indicates that the Diagnostic Code was issued by the Reporting
	MTA.
	In addition to the Diagnostic-Code itself, additional textual description
	of the diagnostic, MAY appear in a comment enclosed in parentheses.
	This field is optional, because some mail systems supply no additional
	information beyond that which is returned in the 'action' and 'status'
	fields. However, this field SHOULD be included if transport-specific
	diagnostic information is available.
	2.3.7 Last-Attempt-Date field
	The Last-Attempt-Date field gives the date and time of the last attempt
	to relay, gateway, or deliver the message (whether successful or
	unsuccessful) by the Reporting MTA. This is not necessarily the same as
	the value of the Date field from the header of the message used to
	transmit this delivery status notification: In cases where the DSN was
	generated by a gateway, the Date field in the message header contains the
	time the DSN was sent by the gateway and the DSN Last-Attempt-Date field
	contains the time the last delivery attempt occurred.
	last-attempt-date-field = "Last-Attempt-Date" ":" date-time
	This field is optional. It MUST NOT be included if the actual date and
	time of the last delivery attempt are not available (which might be the
	case if the DSN were being issued by a gateway).
	The date and time are expressed in RFC 822 'date-time' format, as
	modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
	2.3.8 final-log-id field
	The "final-log-id" field gives the final-log-id of the message that was
	used by the final-mta. This can be useful as an index to the final-mta's
	log entry for that delivery attempt.
	final-log-id-field = "Final-Log-ID" ":" *text
	This field is optional.
	2.3.9 Will-Retry-Until field
	For DSNs of type "delayed", the Will-Retry-Until field gives the date
	after which the Reporting MTA expects to abandon all attempts to deliver
	the message to that recipient. The Will-Retry-Until field is optional for
	"delay" DSNs, and MUST NOT appear in other DSNs.
	will-retry-until-field = "Will-Retry-Until" ":" date-time
	The date and time are expressed in RFC 822 'date-time' format, as
	modified by [HOSTREQ]. Numeric timezones ([+/-]HHMM format) MUST be used.
	2.4 Extension fields
	Additional per-message or per-recipient DSN fields may be defined in the
	future by later revisions or extensions to this specification. Extension-
	field names beginning with "X-" will never be defined as standard fields;
	such names are reserved for experimental use. DSN field names NOT
	beginning with "X-" MUST be registered with the Internet Assigned Numbers
	Authority (IANA) and published in an RFC.
	Extension DSN fields may be defined for the following reasons:
	(a) To allow additional information from foreign delivery status
	reports to be tunneled through Internet DSNs. The names of such
	DSN fields should begin with an indication of the foreign
	environment name (e.g. X400-Physical-Forwarding-Address).
	(b) To allow the transmission of diagnostic information which is
	specific to a particular mail transport protocol. The names of
	such DSN fields should begin with an indication of the mail
	transport being used (e.g. SMTP-Remote-Recipient-Address). Such
	fields should be used for diagnostic purposes only and not by user
	agents or mail gateways.
	(c) To allow transmission of diagnostic information which is specific
	to a particular message transfer agent (MTA). The names of such
	DSN fields should begin with an indication of the MTA
	implementation that produced the DSN. (e.g. Foomail-Queue-ID).
	MTA implementers are encouraged to provide adequate information, via
	extension fields if necessary, to allow an MTA maintainer to understand
	the nature of correctable delivery failures and how to fix them. For
	example, if message delivery attempts are logged, the DSN might include
	information that allows the MTA maintainer to easily find the log entry
	for a failed delivery attempt.
	If an MTA developer does not wish to register the meanings of such
	extension fields, "X-" fields may be used for this purpose. To avoid name
	collisions, the name of the MTA implementation should follow the "X-",
	(e.g. "X-Foomail-Log-ID").
	3. Conformance and Usage Requirements
	An MTA or gateway conforms to this specification if it generates DSNs
	according to the protocol defined in this memo. For MTAs and gateways
	that do not support requests for positive delivery notification (such as
	in [DRPT]), it is sufficient that delivery failure reports use this
	protocol.
	A minimal implementation of this specification need generate only the
	Reporting-MTA per-message field, and the Final-Recipient, Action, and
	Status fields for each attempt to deliver a message to a recipient
	described by the DSN. Generation of the other fields, when appropriate,
	is strongly recommended.
	MTAs and gateways MUST NOT generate the Original-Recipient field of a DSN
	unless the mail transfer protocol provides the address originally
	specified by the sender at the time of submission. (Ordinary SMTP does
	not make that guarantee, but the SMTP extension defined in [DRPT] permits
	such information to be carried in the envelope if it is available.)
	Each sender-specified recipient address SHOULD result in at most one
	"delivered" or "failed" DSN for that recipient. If a positive DSN is
	requested (e.g. one using NOTIFY=SUCCESS in SMTP) for a recipient that is
	forwarded to multiple recipients of an "alias" (as defined in [DRPT],
	section 7.2.7), the forwarding MTA SHOULD normally issue a "expanded" DSN
	for the originally-specified recipient and not propagate the request for
	a DSN to the forwarding addresses. Alternatively, the forwarding MTA MAY
	relay the request for a DSN to exactly one of the forwarding addresses
	and not propagate the request to the others.
	By contrast, successful submission of a message to a mailing list
	exploder is considered final delivery of the message. Upon delivery of a
	message to a recipient address corresponding to a mailing list exploder,
	the Reporting MTA SHOULD issue an appropriate DSN exactly as if the
	recipient address were that of an ordinary mailbox.
	NOTE: This is actually intended to make DSNs usable by mailing lists
	themselves. Any message sent to a mailing list subscriber should
	have its envelope return address pointing to the list maintainer
	[see RFC 1123, section 5.3.7(E)]. Since DSNs are sent to the
	envelope return address, all DSNs resulting from delivery to the
	recipients of a mailing list will be sent to the list maintainer.
	The list maintainer may elect to mechanically process DSNs upon
	receipt, and thus automatically delete invalid addresses from the
	list. (See section 7 of this memo.)
	This specification places no restrictions on the processing of DSNs
	received by user agents or distribution lists.
	4. Security Considerations
	The following security considerations apply when using DSNs:
	4.1 Forgery
	DSNs may be forged as easily as ordinary Internet electronic mail. User
	agents and automatic mail handling facilities (such as mail distribution
	list exploders) that wish to make automatic use of DSNs should take
	appropriate precautions to minimize the potential damage from denial-of-
	service attacks.
	Security threats related to forged DSNs include the sending of:
	(a) A falsified delivery notification when the message is not delivered
	to the indicated recipient,
	(b) A falsified non-delivery notification when the message was in fact
	delivered to the indicated recipient,
	(c) A falsified Final-Recipient address,
	(d) A falsified Remote-MTA identification,
	(e) A falsified relay notification when the message is "dead ended".
	(f) Unsolicited DSNs
	4.2 Confidentiality
	Another dimension of security is confidentiality. There may be cases in
	which a message recipient is autoforwarding messages but does not wish to
	divulge the address to which the messages are autoforwarded. The desire
	for such confidentiality will probably be heightened as "wireless
	mailboxes", such as pagers, become more widely used as autoforward
	addresses.
	MTA authors are encouraged to provide a mechanism which enables the end
	user to preserve the confidentiality of a forwarding address. Depending
	on the degree of confidentiality required, and the nature of the
	environment to which a message were being forwarded, this might be
	accomplished by one or more of:
	(a) issuing a "relayed" DSN (if a positive DSN was requested) when a
	message is forwarded to a confidential forwarding address, and
	disabling requests for positive DSNs for the forwarded message,
	(b) declaring the message to be delivered, issuing a "delivered" DSN, re-
	sending the message to the confidential forwarding address, and
	arranging for no DSNs to be issued for the re-sent message,
	(c) omitting "Remote-*" or extension fields of a DSN whenever they would
	otherwise contain confidential information (such as a confidential
	forwarding address),
	(d) for messages forwarded to a confidential address, setting the
	envelope return address (e.g. SMTP MAIL FROM address) to the NULL
	reverse-path ("<>") (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.
	Implementers are cautioned that many existing MTAs will send non-delivery
	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.
	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.[SMTPDUP] 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.
	5. References
	[DRPT] K. Moore, "SMTP Service Extension for Delivery Status
	Notifications", work-in-progress, University of Tennessee, June 2001.
	[DSN] K. Moore & G. Vaudreuil, "An Extensible Message Format for Delivery
	Status Notifications", RFC 1894, University of Tennessee, Octel Network
	Services, January 1996.
	[HOSTREQ] R. Braden (ed.), "Requirements for Internet Hosts - Application
	and Support", STD 3, RFC 1123, USC/Information Sciences Institute,
	October 1989.
	[MIME1] N. Freed & N. Borenstein, "Multipurpose Internet Mail Extensions
	(MIME) Part One: Format of Internet Message Bodies", RFC 2045, Bellcore,
	Innosoft, November 1996.
	[MIME3] K. Moore, "MIME (Multipurpose Internet Mail Extensions) Part
	Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
	University of Tennessee, November 1996.
	[REPORT] G. Vaudreuil, "The Multipart/Report Content Type for the
	Reporting of Mail System Administrative Messages", Work-in-Progress, June
	2001.
	[RFC822] D. Crocker, "Standard for the format of ARPA Internet Text
	Messages", STD 11, RFC 822, UDEL, August 1982.
	[SMTP] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC 821,
	USC/Information Sciences Institute, August 1982.
	[SMTPDUP] C. Partridge, "Duplicate Messages and SMTP", RFC 1047, BBN,
	February 1988.
	[STATUS] G. Vaudreuil, "Enhanced Mail System Status Codes", Work-in-
	Progress, June 2001.
	6. Copyright Notice
	"Copyright (C) The Internet Society (2002). 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."
	7. Acknowledgments
	The authors wish to thank the following people for their reviews of early
	drafts of RFC 1894 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.
	8. Author's Address
	Keith Moore
	University of Tennessee
	1122 Volunteer Blvd, Suite 203
	Knoxville TN 37996-3450
	USA
	Email: moore@cs.utk.edu
	voice: +1-865-974-3126
	fax: +1-865-974-8296
	Gregory M. Vaudreuil
	Lucent Technologies
	17080 Dallas Parkway
	Dallas, TX 75248-1905
	USA
	Email: GregV@ieee.org
	Voice: +1-972-733-2722
	Appendix A - 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 [HOSTREQ].
	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
	final-log-id-field = "Final-Log-ID" ":" *text
	generic-address = *text
	last-attempt date
	mta-name = *text
	mta-name-type = atom
	original-envelope id
	original-recipient-field =
	"Original-Recipient" ":" address-type ";" generic-address
	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 ]
	[ final-log-id 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 sub-field of the status-code. Each numeric
	; sub-field 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
	Appendix B - 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.
	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.
	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 sub-field 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.
	Appendix C - Guidelines for use of DSNs by mailing list exploders
	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 non-
	delivery reports. A "smart" mailing list exploder can therefore
	intercept such non-delivery 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 might depend on the type of error. On the
	other hand, a "user unknown" error that persisted for several days could
	be considered a reliable indication that address were no longer valid.
	Appendix D - 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 <IANA@IANA.ORG>.
	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.
	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.
	(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]).
	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.
	Appendix E - Examples
	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 sub-field 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.
	Simple DSN
	This is a simple DSN issued after repeated attempts to deliver a message
	failed. In this case, the DSN is issued by the same MTA from which the
	message was originated.
	Date: Thu, 7 Jul 1994 17:16:05 -0400
	From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
	Message-Id: <199407072116.RAA14128@CS.UTK.EDU>
	Subject: Returned mail: Cannot send message for 5 days
	To: <owner-info-mime@cs.utk.edu>
	MIME-Version: 1.0
	Content-Type: multipart/report; report-type=delivery-status;
	boundary="RAA14128.773615765/CS.UTK.EDU"
	--RAA14128.773615765/CS.UTK.EDU
	The original message was received at Sat, 2 Jul 1994 17:10:28 -0400 from
	root@localhost
	----- The following addresses had delivery problems -----
	<louisl@larry.slip.umd.edu> (unrecoverable error)
	----- Transcript of session follows -----
	<louisl@larry.slip.umd.edu>... Deferred: Connection timed out with
	larry.slip.umd.edu. Message could not be delivered for 5 days Message
	will be deleted from queue
	--RAA14128.773615765/CS.UTK.EDU
	content-type: message/delivery-status
	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--
	Multi-Recipient DSN
	This is another DSN issued by the sender's MTA, which contains details of
	multiple delivery attempts. Some of these were detected locally, and
	others by a remote MTA.
	Date: Fri, 8 Jul 1994 09:21:47 -0400
	From: Mail Delivery Subsystem <MAILER-DAEMON@CS.UTK.EDU>
	Subject: Returned mail: User unknown
	To: <owner-ups-mib@CS.UTK.EDU>
	MIME-Version: 1.0
	Content-Type: multipart/report; report-type=delivery-status;
	boundary="JAA13167.773673707/CS.UTK.EDU"
	--JAA13167.773673707/CS.UTK.EDU
	content-type: text/plain; charset=us-ascii
	----- The following addresses had delivery problems -----
	<arathib@vnet.ibm.com> (unrecoverable error) <wsnell@sdcc13.ucsd.edu>
	(unrecoverable error)
	--JAA13167.773673707/CS.UTK.EDU
	content-type: message/delivery-status
	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
	[original message goes here]
	--JAA13167.773673707/CS.UTK.EDU--
	DSN from gateway to foreign system
	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 <AMMGR@corp.timeplex.com>
	Subject: Status of: Re: Battery current sense
	To: owner-ups-mib@CS.UTK.EDU
	Message-id: <01HEGJ0WNBY28Y95LN@mr.timeplex.com>
	MIME-version: 1.0 content-type: multipart/report;
	report-type=delivery-status; boundary="84229080704991.122306.SYS30"
	--84229080704991.122306.SYS30
	content-type: text/plain
	Invalid address - nair_s %DIR-E-NODIRMTCH, No matching Directory Entry
	found
	--84229080704991.122306.SYS30
	content-type: message/delivery-status
	Reporting-MTA: mailbus; SYS30
	Final-Recipient: unknown; nair_s
	Status: 5.0.0 (unknown permanent failure)
	Action: failed
	--84229080704991.122306.SYS30--
	Delayed DSN
	A delay report from a multiprotocol MTA. Note that there is no returned
	content, so no third body part appears in the DSN.
	MIME-Version: 1.0
	From: <postmaster@nsfnet-relay.ac.uk>
	Message-Id: <199407092338.TAA23293@CS.UTK.EDU>
	Received: from nsfnet-relay.ac.uk by sun2.nsfnet-relay.ac.uk
	id: <g.12954-0@sun2.nsfnet-relay.ac.uk>;
	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		Title: An Extensible Message Format for Delivery Status
	content-type: message/delivery-status		Notifications
			Author(s): K. Moore, G. Vaudreuil
			Status: Standards Track
			Date: January 2003
			Mailbox: moore@cs.utk.edu, GregV@ieee.org
			Pages: 40
			Characters: 83060
			Obsoletes: 1894
	Reporting-MTA: dns; sun2.nsfnet-relay.ac.uk		I-D Tag: draft-vaudreuil-1894bis-02.txt
	Final-Recipient: rfc822;thomas@de-montfort.ac.uk		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3464.txt
	Status: 4.0.0 (unknown temporary failure)
	Action: delayed
	--foobar--		This memo defines a Multipurpose Internet Mail Extensions (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.
	Appendix F - Changes from RFC1894		Because many messages are sent between the Internet and other
			messaging systems (such as X.400 or the so-called "Local Area Network
			(LAN)-based" systems), the Delivery Status Notification (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.
	Changed Authors contact information		This is now a Draft Standard Protocol.
	Updated required standards boilerplate		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.
	Edited the text to make it spell-checker and grammar checker compliant		This announcement is sent to the IETF list and the RFC-DIST list.
			Requests to be added to or deleted from the IETF distribution list
			should be sent to IETF-REQUEST@IETF.ORG. Requests to be
			added to or deleted from the RFC-DIST distribution list should
			be sent to RFC-DIST-REQUEST@RFC-EDITOR.ORG.
	Updated references to point to later, more mature documents, changed		Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
	reference enumeration scheme.		an EMAIL message to rfc-info@RFC-EDITOR.ORG with the message body
			help: ways_to_get_rfcs. For example:
	Fixed Delayed DSN example		To: rfc-info@RFC-EDITOR.ORG
			Subject: getting rfcs
	Added Table of Contents		help: ways_to_get_rfcs
	Moved Appendix's to the end of the document		Requests for special distribution should be addressed to either the
			author of the RFC in question, or to RFC-Manager@RFC-EDITOR.ORG. Unless
			specifically noted otherwise on the RFC itself, all RFCs are for
			unlimited distribution.echo
			Submissions for Requests for Comments should be sent to
			RFC-EDITOR@RFC-EDITOR.ORG. Please consult RFC 2223, Instructions to RFC
			Authors, for further information.
End of changes. 14 change blocks.
	1664 lines changed or deleted		46 lines changed or added
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