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: <[email protected]> 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;[email protected] Final-Recipient: rfc822;[email protected] 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;[email protected] Final-Recipient: rfc822;[email protected] Action: failed Status: 5.0.0 (permanent failure) Diagnostic-Code: smtp; 550 '[email protected]' is not a registered gateway user Remote-MTA: dns; vnet.ibm.com Original-Recipient: rfc822;[email protected] Final-Recipient: rfc822;[email protected] Action: delayed Status: 4.0.0 (hpnjld.njd.jp.com: host name lookup failure) Original-Recipient: rfc822;[email protected] Final-Recipient: rfc822;[email protected] 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: [email protected] Message-id: <[email protected]> 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: <[email protected]> Received: from nsfnet-relay.ac.uk by sun2.nsfnet-relay.ac.uk id ; Sun, 10 Jul 1994 00:36:51 +0100 To: [email protected] 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: [email protected] 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;[email protected] 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: [email protected] 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: [email protected] Moore & Vaudreuil Standards Track [Page 39]