Network Working Group Keith Moore Internet-Draft University of Tennessee Expires: 12 September 1995 12 March 1995 SMTP Service Extension for Delivery Status Notifications draft-ietf-notary-smtp-drpt-03.txt 1. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). 2. Abstract This memo defines an extension to the SMTP service, which allow an SMTP client to specify (a) that delivery status notifications (DSNs) should be generated under certain conditions, (b) whether such notifications should return the contents of the message, and (c) additional information, to be returned with a DSN, that allows the sender to identify both the recipient(s) for which the DSN was issued, and the transaction in which the original message was sent. 3. Introduction The SMTP protocol [1] requires that an SMTP server provide notification of delivery failure, if it determines that a message cannot be delivered to one or more recipients. Traditionally, such notification consists of an ordinary Internet mail message (format defined by [2]), sent to the envelope sender address (the argument of the SMTP MAIL command), containing an explanation of the error and at least the headers the failed message. Experiences with large mail distribution lists [3] indicates that such messages are often insufficient to diagnose problems, or even to determine at which host or for which recipients a problem occurred. In addition, the lack of a standardized format for delivery notifications K. Moore Expires 12 September 1995 [Page 1] SMTP Delivery Status Notifications 12 March 1995 in Internet mail makes it difficult to exchange such notifications with other message handling systems. Such experience has demonstrated a need for a delivery status notification service for Internet electronic mail, which: (a) is reliable, in the sense that any DSN request will either be honored at the time of final delivery, or result in a response that indicates that the request cannot be honored, (b) should result in exactly one response for any particular sender- specified recipient, (c) is stable, in that a DSN should never be issued in response to a DSN, (d) preserves sufficient information to allow the sender to identify both the mail transaction and the recipient address which caused the notification, even when mail is forwarded or gatewayed to foreign environments, and (e) interfaces acceptably with non-SMTP and non-822-based mail systems, both so that notifications returned from foreign mail systems may be useful to Internet users, and so that the notification requests from foreign environments may be honored. Among the requirements implied by this goal are the ability to request non-return-of-content, and the ability to specify whether positive delivery notifications, negative delivery notifications, both, or neither, should be issued. In an attempt to provide such a service, this memo uses the mechanism defined in [4] to define an extension to the SMTP protocol. Using this mechanism, an SMTP client may request that an SMTP server issue or not issue a delivery status notification (DSN) under certain conditions. The format of a DSN is defined in [5]. 4. Framework for the Delivery Status Notification Extension The following service extension is therefore defined: (1) The name of the SMTP service extension is "Delivery Status Notification"; (2) the EHLO keyword value associated with this extension is "DSN", the meaning of which is defined in section 5 of this memo; (3) no parameters are allowed with this EHLO keyword value; (4) two optional parameters are added to the RCPT command, and two optional parameters are added to the MAIL command: K. Moore Expires 12 September 1995 [Page 2] SMTP Delivery Status Notifications 12 March 1995 An optional parameter for the RCPT command, using the esmtp-keyword "NOTIFY", (to specify the conditions under which a delivery status notification should be generated), is defined in section 6.1, An optional parameter for the RCPT command, using the esmtp-keyword "ORCPT", (used to convey the "original" (sender-specified) recipient address), is defined in section 6.2, and An optional parameter for the MAIL command, using the esmtp-keyword "RET", (to request that DSNs either return or not return the contents of a message), is defined in section 6.3, An optional parameter for the MAIL command, using the esmtp-keyword "ENVID", (used to propagate a sender-specified unique identifier for this envelope, to be returned in a DSN), is defined in section 6.4; (5) no additional SMTP verbs are defined by this extension. The remainder of this memo specifies how support for the extension affects the behavior of a message transfer agent. 5. The Delivery Status Notification service extension An SMTP client wishing to request a DSN for a message may issue the EHLO command to start an SMTP session, to determine if the server supports any of several service extensions. If the server responds with code 250 to the EHLO command, and the response includes the EHLO keyword DSN, then the Delivery Status Notification extension (as described in this memo) is supported. Ordinarily, when an SMTP server returns a positive (2xx) reply code in response to a RCPT command, it agrees to accept responsibility for either delivering the message to the named recipient, or sending a notification to the sender of the message indicating that delivery has failed. However, an extended SMTP ("ESMTP") server which implements this service extension will accept an optional NOTIFY parameter with the RCPT command. If present, the NOTIFY parameter alters the default conditions for generation of delivery status notifications from the default (issue notifications only on failure) specified in [1]. The ESMTP client may also request (via the RET parameter) whether the entire contents of the original message should be returned (as opposed to just the headers of that message), along with the DSN. In general, an ESMTP server which implements this service extension will propagate delivery status notification requests when relaying mail to other SMTP-based MTAs which also support this extension, and make a "best effort" to ensure that such requests are honored when messages are passed into other environments. K. Moore Expires 12 September 1995 [Page 3] SMTP Delivery Status Notifications 12 March 1995 In order that any delivery status notifications thus generated will be meaningful to the sender, any ESMTP server which supports this extension will attempt to propagate the following information to any other MTAs that are used to relay the message, for use in generating DSNs: (a) for each recipient, a copy of the original recipient address, as used by the sender of the message. This address need not be the same as the mailbox specified in the RCPT command. For example, the addresses will be different if the message was forwarded from the sender-specified address to another address, or the message originated in a foreign environment that does not use Internet electronic mail addresses. (b) for the entire SMTP transaction, an envelope identification string, which may be used by the sender to associate any delivery status notifications with the transaction used to send the original message. 6. Additional parameters for RCPT and MAIL commands The extended RCPT and MAIL commands are issued by a client when it wishes to request a DSN from the server, under certain conditions, for a particular recipient. The extended RCPT and MAIL commands are identical to the RCPT and MAIL commands defined in [1], except that one or more of the following parameters appear after the sender or recipient address, respectively. The general syntax for extended SMTP commands is defined in [4]. 6.1. The NOTIFY parameter of the ESMTP RCPT command A RCPT command issued by a client may contain the optional esmtp- keyword "NOTIFY", to specify the conditions under which the SMTP server should generate DSNs for that recipient. If the NOTIFY esmtp-keyword is used, it MUST have an associated esmtp-value, formatted according to the following rules, using the ABNF of RFC 822: notify-esmtp-value = "NEVER" / 1#notify-list-element notify-list-element = "SUCCESS" / "FAILURE" / "DELAY" Notes: a. Multiple notify-list-elements, separated by commas, MAY appear in a NOTIFY parameter; however, the NEVER keyword MUST appear by itself. b. Any of the keywords NEVER, SUCCESS, FAILURE, or DELAY may be spelled in any combination of upper and lower case letters. K. Moore Expires 12 September 1995 [Page 4] SMTP Delivery Status Notifications 12 March 1995 c. Although RFC 822 ABNF syntax is used, white space MUST NOT be transmitted within an notify-esmtp-value, and RFC 822 style comments MUST NOT appear in NOTIFY parameter values. The meaning of the NOTIFY parameter values is generally as follows: + An NOTIFY parameter value of "NEVER" requests that a DSN not be issued under any conditions. + A NOTIFY parameter value containing the "SUCCESS" or "FAILURE" keywords requests that a DSN be issued on successful delivery or delivery failure, respectively. + A NOTIFY parameter value containing the keyword "DELAY" indicates the sender's willingness to received "delayed" DSNs. Delayed DSNs may be issued if delivery of a message has been delayed for an unusual amount of time (as determined by the MTA at which the message is delayed), but the final delivery status (whether successful or failure) cannot be determined. The absence of the DELAY keyword in a NOTIFY parameter requests that a "delayed" DSN NOT be issued under any conditions. The actual rules governing interpretation of the NOTIFY parameter are given in section 7. If the NOTIFY parameter is not included in a RCPT command, the SMTP server should issue notifications for that recipient only if the message cannot be delivered, as specified in [1]. 6.2 The ORCPT parameter to the ESMTP RCPT command The ORCPT esmtp-keyword of the RCPT command is used to specify an "original" recipient address that corresponds to the actual recipient to which the message is to be delivered. If the ORCPT esmtp-keyword is used, it MUST have an associated esmtp-value, which consists of the original recipient address, encoded according to the rules below. The ABNF for the ORCPT parameter is: orcpt-parameter = "ORCPT=" original-recipient-address original-recipient-address = addr-type ";" xtext where "addr-type" and "xtext" are defined in [5]. "addr-type" must be an IANA-registered electronic mail address type, while "xtext" contains a representation of the original recipient address, encoded according to the rules for "xtext" in [5]. NOTE: The syntax for "esmtp-value" in [4] does not allow SP, "=", control characters, or non-ASCII characters to be transmitted in an esmtp-value. If any of these characters appear in the original recipient address, their octet values must be encoded in hexadecimal K. Moore Expires 12 September 1995 [Page 5] SMTP Delivery Status Notifications 12 March 1995 according to the rules for "xtext". Because a message may have originated in a foreign environment that does not use Internet-style electronic mail addresses, the esmtp-value associated with the ORCPT keyword is NOT constrained to conform to syntax rules for Internet addresses. Instead, the "addr-type" portion of the original-recipient-address is used to identify the "type" of address which appears in the ORCPT parameter value. Ideally, the "xtext" portion of the original-recipient-address should contain, in encoded form, the same sequence of characters that the sender used to specify the recipient. However, for a message gatewayed from an environment (such as X.400) in which a recipient address is not a simple string of printable characters, the ORCPT parameter should contain a printable representation of the recipient address that is likely to be recognized by the sender. 6.2 The RET parameter of the ESMTP MAIL command The RET esmtp-keyword on the extended MAIL command specifies whether or not the message should be included in any DSN issued for this message transmission. If the RET esmtp-keyword is used, it MUST have an associated esmtp-value, which is one of the following keywords: FULL requests that the entire message be returned in any delivery status notification issued for this recipient. HDRS requests that only the headers of the message be returned. 6.3 The ENVID parameter to the ESMTP MAIL command The ENVID esmtp-keyword of the SMTP MAIL command is used to specify an "envelope identifier" to be transmitted along with the message and included in any DSNs issued for any of the recipients named in this SMTP transaction. The purpose of the envelope identifier is to allow the sender of a message to identify the transaction for which the DSN was issued. The ABNF for the ENVID parameter is: envid-parameter = "ENVID=" xtext The ENVID esmtp-keyword MUST have an associated esmtp-value. No meaning is assigned by the mail system to the presence or absence of this parameter or to any esmtp-value associated with this parameter; the information is used only by the sender or his user agent. K. Moore Expires 12 September 1995 [Page 6] SMTP Delivery Status Notifications 12 March 1995 6.4 Restrictions on the use of Delivery Status Notification parameters The RET and ENVID parameters MUST NOT appear more than once each in any single MAIL command. If more than one of either of these parameters appears in a MAIL command, the ESMTP server SHOULD respond with "501 syntax error in parameters or arguments". The NOTIFY and ORCPT parameters MUST NOT appear more than once in any RCPT command. If more than one of either of these parameters appears in a RCPT command, the ESMTP server SHOULD respond with "501 syntax error in parameters or arguments". 7. Conformance requirements The Simple Message Transfer Protocol (SMTP) is used by both Message Transfer Agents (MTAs) when accepting, relaying, or gatewaying mail, as well as User Agents (UAs) when submitting mail to the mail transport system. The DSN extension to SMTP may be used to allow UAs to convey the sender's requests as to when DSNs should be issued. A UA which claims to conform to this specification must meet certain requirements as described below. Typically, a message transfer agent (MTA) which supports SMTP will assume, at different times, both the role of a SMTP client and an SMTP server, and may also provide local delivery, gatewaying to foreign environments, forwarding, and mailing list expansion. An MTA which, when acting as an SMTP server, issues the DSN keyword in response to the EHLO command, MUST obey the rules below for a "conforming SMTP client" when acting as a client, and a "conforming SMTP server" when acting as a server. The term "conforming MTA" refers to an MTA which conforms to this specification, independent of its role of client or server. 7.1 SMTP protocol interactions The following rules apply to SMTP transactions in which any of the ENVID, NOTIFY, RET, or ORCPT keywords are used: (a) If an SMTP client issues a MAIL command containing a valid ENVID parameter and associated esmtp-value and/or a valid RET parameter and associated esmtp-value, a conforming SMTP server MUST return the same reply-code as it would to the same MAIL command without the ENVID and/or OMTS parameters. A conforming SMTP server MUST NOT refuse a MAIL command based on the absence or presence of valid ENVID or RET parameters, or on their associated esmtp-values. However, if the associated esmtp-keyword is not valid (i.e. contains illegal characters), or if there is more than one ENVID or RET parameter in a particular MAIL command, the server SHOULD issue the response "501 syntax error in parameter". K. Moore Expires 12 September 1995 [Page 7] SMTP Delivery Status Notifications 12 March 1995 (b) If an SMTP client issues a RCPT command containing any valid NOTIFY and/or ORCPT parameters, a conforming SMTP server MUST return the same response as it would to the same RCPT command without those NOTIFY and/or ORCPT parameters. A conforming SMTP server MUST NOT refuse a RCPT command based on the presence or absence of any of these parameters. However, if any of the associated esmtp-keywords are not valid, or if there is more than one of any of these parameters in a particular RCPT command, the server SHOULD issue the response "501 syntax error in parameter". 7.2. Handling of messages received via SMTP This section describes how a conforming MTA should handle any messages received via SMTP. 7.2.1. Relay of messages to other conforming SMTP servers The following rules govern the behavior of a conforming MTA, when relaying a message which was received via the SMTP protocol, to an SMTP server that supports the Delivery Status Notification service extension: (a) Any ENVID parameter included in the MAIL command when a message was received, MUST also appear on the MAIL command with which the message is relayed, with the same associated esmtp-value. If no ENVID parameter was included in the MAIL command when the message was received, the ENVID parameter MUST NOT be supplied when the message is relayed. (b) Any RET parameter included in the MAIL command when a message was received, MUST also appear on the MAIL command with which the message is relayed, with the same associated esmtp-value. If no RET parameter was included in the MAIL command when the message was received, the RET parameter MUST NOT supplied when the message is relayed. (c) If the NOTIFY parameter was supplied for a recipient when the message was received, the RCPT command issued when the message is relayed MUST also contain the NOTIFY parameter along with its associated esmtp-value. If no NOTIFY parameter was supplied for a recipient when the message was received, the NOTIFY parameter MUST NOT be supplied for that recipient when the message is relayed. (d) If any ORCPT parameter was present in the RCPT command for a recipient when the message was received, that parameter and its associated value MUST appear in the RCPT command issued for that recipient when relaying the message. K. Moore Expires 12 September 1995 [Page 8] SMTP Delivery Status Notifications 12 March 1995 If no ORCPT parameter was present in the RCPT command when the message was received, an ORCPT parameter MAY be added to the RCPT command when the message is relayed. If an ORCPT parameter is added by the relaying MTA, it MUST contain the recipient address from the RCPT command used when the message was received by that MTA. 7.2.2. Relay of messages to non-conforming SMTP servers The following rules govern the behavior of a conforming MTA (in the role of client), when relaying a message which was received via the SMTP protocol, to an SMTP server that does not support the Delivery Status Notification service extension: (a) ENVID, NOTIFY, RET, or ORCPT parameters MUST NOT be issued when relaying the message. (b) If the NOTIFY parameter was supplied for a recipient, with an esmtp- value containing the keyword SUCCESS, and the SMTP server returns a success (2XX) reply-code in response to the RCPT command, the client MUST issue a "relayed" DSN for that recipient. (c) If the NOTIFY parameter was supplied for a recipient with an esmtp- value containing the keyword FAILURE, and the SMTP server returns a permanent failure (5XX) reply-code in response to the RCPT command, the client MUST issue a "failed" DSN for that recipient. (d) If the NOTIFY parameter was supplied for a recipient with an esmtp- value of NEVER, the client MUST NOT issue a DSN for that recipient, regardless of the reply-code returned by the SMTP server. When attempting to relay a message to an SMTP server that does not support this extension, and if NOTIFY=NEVER was specified for some recipients of that message, a conforming SMTP client MAY relay the message for those recipients in a separate SMTP transaction, using an empty reverse-path in the MAIL command. This will prevent DSNs from being issued for those recipients by MTAs that conform to [1]. (e) If a NOTIFY parameter was not supplied for a recipient, and the SMTP server returns a success (2XX) reply-code in response to a RCPT command, the client MUST NOT issue any DSN for that recipient. (f) If a NOTIFY parameter was not supplied for a recipient, and the SMTP server returns a permanent failure (5XX) reply-code in response to a RCPT command, the client MUST issue a "failed" DSN for that recipient. K. Moore Expires 12 September 1995 [Page 9] SMTP Delivery Status Notifications 12 March 1995 7.2.3. Local delivery of messages The following rules govern the behavior of a conforming MTA upon successful delivery of a message that was received via the SMTP protocol, to a local recipient's mailbox: (a) If the NOTIFY parameter was supplied for that recipient, with an esmtp-value containing the SUCCESS keyword, the MTA MUST issue a "delivered" DSN for that recipient. (b) If the NOTIFY parameter was supplied for that recipient with an esmtp-value of NEVER, the MTA MUST NOT issue a DSN for that recipient. (c) If the NOTIFY parameter was not supplied for that recipient, the MTA MUST NOT issue a DSN. 7.2.4. Gatewaying a message into a foreign environment The following rules govern the behavior of a conforming MTA, when gatewaying a message that was received via the SMTP protocol, into a foreign (non-SMTP) environment: (a) If the the foreign environment is capable of issuing appropriate notifications under the conditions requested by the NOTIFY parameter, and the conforming MTA can ensure that any notification thus issued will be translated into a DSN and delivered to the original sender, then the MTA SHOULD gateway the message into the foreign environment, requesting notification under the desired conditions, without itself issuing a DSN. (b) If a NOTIFY parameter was supplied with either or both of the SUCCESS or FAILURE keywords, but the requested conditions specified by the associated esmtp-value cannot be met by the foreign mail environment, the MTA SHOULD issue a "relayed" DSN for that recipient. (c) If a NOTIFY parameter was supplied with an esmtp-keyword of NEVER, a DSN MUST NOT be issued. If possible, the MTA SHOULD direct the destination environment to not issue delivery notifications for that recipient. (d) If the NOTIFY parameter was not supplied for a particular recipient, a DSN SHOULD NOT be issued by the gateway. The gateway SHOULD attempt to ensure that appropriate notification will be provided by the foreign mail environment if eventual delivery failure occurs, and that no notification will be issued on successful delivery. (e) When gatewaying a message into a foreign environment, the return-of- content conditions specified by any RET parameter are nonbinding; K. Moore Expires 12 September 1995 [Page 10] SMTP Delivery Status Notifications 12 March 1995 however, the MTA SHOULD attempt to honor the request using whatever mechanisms exist in the foreign environment. 7.2.5. Delays in delivery A conforming MTA which receives a message via the SMTP protocol which is unable to deliver or relay a message to one or more recipients for an extended length of time (to be determined by the MTA), MAY issue a "delayed" DSN for those recipients, under the following conditions: (a) If the NOTIFY parameter was supplied for a recipient and its value included the DELAY keyword, a "delayed" DSN MAY be issued. (b) If the NOTIFY parameter was not supplied for a recipient, a "delayed" DSN MAY be issued. (c) If the NOTIFY parameter was supplied which did not contain the DELAY keyword, a "delayed" DSN MUST NOT be issued. NOTE: Although delay notifications are common in present-day email, a conforming MTA is never required to issue "delayed" DSNs. The DELAY keyword of the NOTIFY parameter is provided to allow the SMTP client to specifically request (by omitting the DELAY parameter) that "delayed" DSNs NOT be issued. 7.2.6. Failure of a conforming MTA to deliver a message The following rules govern the behavior of a conforming MTA which received a message via the SMTP protocol, and is unable to deliver a message to a recipient specified in the SMTP transaction: (a) If a NOTIFY parameter was supplied for the recipient with an esmtp- keyword containing the value FAILURE, a "failed" DSN MUST be issued by the MTA. (b) If a NOTIFY parameter was supplied for the recipient which did not contain the value FAILURE, a DSN MUST NOT be issued for that recipient. (c) If no NOTIFY parameter was supplied for the recipient, a "failure" DSN MUST be issued. 7.2.7. Recipient-specified mail forwarding If a message intended for a particular recipient address is to be "forwarded" to EXACTLY one recipient address: (a) If the message is forwarded to an SMTP server that supports this K. Moore Expires 12 September 1995 [Page 11] SMTP Delivery Status Notifications 12 March 1995 extension, any ENVID, RET, NOTIFY, and ORCPT parameters included with the message as received SHOULD be propagated with the forwarded message. (b) If no ORCPT parameter was supplied for that recipient when the message was received, and the message is being forwarded to an SMTP server which supports this extension, the MTA SHOULD supply an ORCPT parameter. If supplied, the ORCPT parameter MUST contain the recipient's address as it appeared in the envelope (e.g. SMTP RCPT command) in which the message was received. (c) If the message is being forwarded to a non-SMTP environment, or an SMTP server that does not support this extension, the forwarding MTA should, if possible, honor the sender's requests for when delivery notifications should be issued by the destination environment. If the sender's request for either a positive or negative delivery notification cannot be honored, the MTA MUST issue a "relayed" notification. If the message is to be forwarded to multiple recipient addresses on behalf of a single recipient, and the sender has requested that positive DSNs be issued, the MTA MUST either (a) issue a "delivered" DSN for that recipient, and arrange that no DSNs be issued for any of the forwarding addresses for that recipient; or (b) propagate the sender's request for a positive and/or negative DSN to exactly one of the forwarding addresses, and arrange that no DSNs are issued for the other recipient addresses. NOTE: This is intended to ensure that at most one DSN be issued per recipient of a message. DSNs will be difficult to use by mailing list managers if it is possible to receive more than one notification per recipient (e.g. if a message were forwarded to two recipients, and delivery succeeded for one and failed for the other). However, it is still possible to get both a "relayed" or "delivered" DSN and afterwards a "failed" DSN for the same recipient, and a foreign mail system might not issue DSNs for forwarded messages and deliveries to lists. 7.2.8. Delivery of a message to a mailing list If a particular recipient address refers to a mailing list, a message is considered to be successfully delivered to that recipient if the MTA determines that the message is eligible to be distributed to the members of the list. If a NOTIFY parameter was supplied with an esmtp-value which contains the value SUCCESS, a "delivered" DSN MUST be issued. Any envelope-id, original-mts-type, notify-request, return-of-content- request, or original-recipient-address MUST NOT be propagated when delivering a message to the recipients of that list. If the message is not eligible to be distributed to the list membership (perhaps because the sender is not authorized), and either a K. Moore Expires 12 September 1995 [Page 12] SMTP Delivery Status Notifications 12 March 1995 NOTIFY parameter was supplied which contained the FAILURE keyword, or no NOTIFY parameter was supplied, a "failed" DSN MUST be issued. 7.2.9. DSNs describing delivery to multiple recipients A single DSN may describe attempts to deliver a message to multiple recipients of that message. If a DSN is issued for some recipients in an SMTP transaction and not for others according to the rules above, the DSN SHOULD NOT contain information for recipients for whom DSNs would not otherwise have been issued. 7.3. Handling of messages from other sources For messages which originated from "local" users (whatever that means), the specifications under which DSNs should be generated can be communicated to the MTA via any protocol agreed on between the sender's mail composer (user agent) and the MTA. The local MTA can then either relay the message, or issue appropriate delivery status notifications. However, if such requests are transmitted within the message itself (for example in the message headers), the requests MUST be removed from the message before it is transmitted via SMTP. For messages gatewayed from non-SMTP sources and further relayed by SMTP, the gateway SHOULD, using the SMTP extensions described here, attempt to provide the delivery reporting conditions expected by the source mail environment. If appropriate, any DSNs returned to the source environment SHOULD be translated into the format expected in that environment. 8. Format of delivery notifications The format of delivery status notifications is defined in [5], which uses the framework defined in [6]. Delivery status notifications are to be returned to the sender of the original message according as outlined below. 8.1. SMTP Envelope to be used with delivery status notifications The sender address (in the SMTP MAIL command) MUST be an null reverse-path ("<>"), as required by section 5.3.3 of [7]. The recipient address (in the RCPT command) is copied from the MAIL command which accompanied the message for which the DSN is being issued. When transmitting a DSN via SMTP, the ENVID, RET, and ORCPT parameters MUST NOT be used. The NOTIFY parameter MAY be used, but its value must be NEVER. K. Moore Expires 12 September 1995 [Page 13] SMTP Delivery Status Notifications 12 March 1995 8.2. Contents of the DSN A DSN is transmitted as a MIME message with a top-level content-type of multipart/report (as defined in [5]). The multipart/report content-type may be used for any of several kinds of reports generated by the mail system. When multipart/report is used to convey a DSN, the report-type parameter of the multipart/report content-type is "delivery-status". As described in [6], the first component of a multipart/report content-type is a human readable explanation of the report. For a DSN, the second component of the multipart/report is of content-type message/delivery-status (defined in [5]). The third component of the multipart/report consists of the returned message (or only the headers). 8.3. Message/delivery-status fields The multipart/delivery-status content-type defines a number of fields, with general specifications for their contents. The following requirements for any DSNs generated in response to a message received by the SMTP protocol by a conforming SMTP server, are in addition to the requirements defined in [5] for the multipart/delivery-status type. When generating a DSN for a message which was received via the SMTP protocol, a conforming MTA will generate the following fields of the multipart/delivery-status body part: (a) if an ENVID parameter was present on the MAIL command, an Original- Envelope-ID field MUST be supplied, and the value associated with the ENVID parameter must appear in that field. If the message was received via SMTP with no ENVID parameter, the Original-Envelope-ID field MUST NOT be supplied. Since the ENVID parameter will already be encoded as 'xtext', the MTA can simply copy the ENVID value to the Original-Envelope-ID field without further encoding. (b) The Reporting-MTA field MUST be supplied. It should contain the domain name of the SMTP server which is actually issuing this notification (encoded as 'xtext'). The MTA-name-type subfield should be "dns". (c) Other per-message fields as defined in [5] MAY be supplied as appropriate. (d) If the ORCPT parameter was provided for this recipient, the Original-Recipient field MUST be supplied, with its value taken from the ORCPT parameter. If no ORCPT parameter was provided for this recipient, the Original-Recipient field MUST NOT appear. (e) The Final-Recipient field MUST be supplied. It MUST contain the K. Moore Expires 12 September 1995 [Page 14] SMTP Delivery Status Notifications 12 March 1995 recipient address from the message envelope, encoded according to the rules for 'xtext'. If the message was received via SMTP, the address-type will be "rfc822". (f) The Action field MUST be supplied. (g) The Status field MUST be supplied, using a status-code from [8]. If there is no specific code which suitably describes a delivery failure, either 4.0.0 (temporary failure), or 5.0.0 (permanent failure) must be used. (h) For DSNs resulting from attempts to relay a message to one or more recipients via SMTP, the Remote-MTA field MUST be supplied for each of those recipients. The mta-name-type subfields of those Remote- MTA fields will be "dns". (i) For DSNs resulting from attempts to relay a message to one or more recipients via SMTP, the Diagnostic-Code MUST be supplied for each of those recipients. The diagnostic-type subfields will be "smtp", and the "xtext" MUST contain the numeric SMTP reply-code received from the SMTP server. The text accompanying the SMTP reply-code MAY appear in a comment. (j) For DSNs resulting from attempts to relay a message to one or more recipients via SMTP, an SMTP-Remote-Recipient extension field MAY be supplied for each recipient, which contains the address of that recpient which was presented to the remote SMTP server. (k) Other per-recipient fields defined in [5] MAY appear, as appropriate. 9. Acknowledgments The author wishes to thank Eric Allman, Harald Alvestrand, Jim Conklin, Peter Cowen, Dave Crocker, Ned Freed, Steve Kille, John Klensin, John Gardiner Myers, Julian Onions, Jacob Palme, Marshall Rose, and Greg Vaudreuil for their suggestions for improvement of this document. 10. Appendix - Type-Name Definitions The following type names are defined for use in DSN fields generated by conforming SMTP-based MTAs: 10.1 "rfc822" address-type The "rfc822" address-type is to be used when reporting Internet electronic mail address in the Original-Recipient and Final-Recipient K. Moore Expires 12 September 1995 [Page 15] SMTP Delivery Status Notifications 12 March 1995 DSN fields. Addresses of this address-type are generally expected to be of the form: [route] addr-spec where "route" and "addr-spec" are defined in [2], and the "domain" portions of both "route" and "addr-spec" are fully-qualified domain names that are registered in the DNS. However, MTAs MUST NOT attempt to "correct" an address that is reported in a DSN, even if it does not conform to the syntax rules. 10.2 "smtp" diagnostic-type The "smtp" diagnostic-type is to be used when reporting SMTP 3-digit reply-codes in Diagnostic-Code DSN fields. SMTP reply-codes are currently defined in [1], [4], and [7]. Additional codes may be defined by other RFCs. Only the 3-digit reply code is to be reported as the Diagnostic-Code. However, any text accompanying the reply-code MAY appear as a comment enclosed in parentheses. 10.3 "dns" MTA-name-type The "dns" MTA-name-type should be used in the Reporting-MTA field. An MTA-name of type "dns" is a fully-qualified domain name. The name must be registered in the DNS, and the address Postmaster@{mta-name} must be valid. 11. Appendix - Example This example traces the flow of a single message addressed to multiple recipients. The message is sent by Alice@Pure-Heart.ORG to Bob@Big-Bucks.COM, Carol@Ivory.EDU, Dana@Ivory.EDU, Eric@Bombs.AF.MIL, Fred@Bombs.AF.MIL, and George@Tax-ME.GOV, with a variety of per- recipient options. The message is successfully delivered to Bob, Dana (via a gateway), Eric, and Fred. Delivery fails for Carol and George. K. Moore Expires 12 September 1995 [Page 16] SMTP Delivery Status Notifications 12 March 1995 11.1 Submission Alice's user agent sends the message to the SMTP server at Pure- Heart.ORG. Note that while this example uses SMTP as a mail submission protocol, other protocols could also be used. <<< 220 Pure-Heart.ORG SMTP server here >>> EHLO Pure-Heart.ORG <<< 250-Pure-Heart.ORG <<< 250-DSN <<< 250-EXPN <<< 250 SIZE >>> MAIL FROM: RET=HDRS ENVID=QQ314159 <<< 250 sender ok >>> RCPT TO: NOTIFY=SUCCESS ORCPT=Bob@Big-Bucks.COM <<< 250 recipient ok >>> RCPT TO: NOTIFY=FAILURE ORCPT=Carol@Ivory.EDU <<< 250 recipient ok >>> RCPT TO: NOTIFY=SUCCESS,FAILURE ORCPT=Dana@Ivory.EDU <<< 250 recipient ok >>> RCPT TO: NOTIFY=FAILURE ORCPT=Eric@Bombs.AF.MIL <<< 250 recipient ok >>> RCPT TO: NOTIFY=NEVER <<< 250 recipient ok >>> RCPT TO: NOTIFY=FAILURE ORCPT=George@Tax-ME.GOV <<< 250 recipient ok >>> DATA <<< 354 okay, send message >>> (message goes here) >>> . <<< 250 message accepted >>> QUIT <<< 221 goodbye K. Moore Expires 12 September 1995 [Page 17] SMTP Delivery Status Notifications 12 March 1995 11.2 Relay to Big-Bucks.COM The SMTP at Pure-Heart.ORG then relays the message to Big-Bucks.COM. (For the purpose of this example, mail.Big-Bucks.COM is the primary mail exchanger for Big-Bucks.COM). <<< 220 mail.Big-Bucks.COM says hello >>> EHLO Pure-Heart.ORG <<< 250-mail.Big-Bucks.COM <<< 250 DSN >>> MAIL FROM: RET=HDRS ENVID=QQ314159 <<< 250 sender okay >>> RCPT TO: NOTIFY=SUCCESS ORCPT=Bob@Big-Bucks.COM <<< 250 recipient okay >>> DATA <<< 354 send message >>> (message goes here) >>> . <<< 250 message received >>> QUIT <<< 221 bcnu K. Moore Expires 12 September 1995 [Page 18] SMTP Delivery Status Notifications 12 March 1995 11.3 Relay to Ivory.EDU The SMTP at Pure-Heart.ORG relays the message to Ivory.EDU, which (as it happens) is a gateway to a LAN-based mail system that accepts SMTP mail and supports the DSN extension. <<< 220 Ivory.EDU gateway to FooMail(tm) here >>> EHLO Pure-Heart.ORG <<< 250-Ivory.EDU <<< 250 DSN >>> MAIL FROM: RET=HDRS ENVID=QQ314159 <<< 250 ok >>> RCPT TO: NOTIFY=FAILURE ORCPT=Carol@Ivory.EDU <<< 550 error - no such recipient >>> RCPT TO: NOTIFY=SUCCESS,FAILURE ORCPT=Dana@Ivory.EDU <<< 250 recipient ok >>> DATA <<< 354 send message, end with '.' >>> (message goes here) >>> . <<< 250 message received >>> QUIT <<< 221 bye Note that since the Ivory.EDU refused to accept mail for Carol@Ivory.EDU, and the sender specified NOTIFY=FAILURE, the sender- SMTP (in this case Pure-Heart.ORG) must generate a DSN. K. Moore Expires 12 September 1995 [Page 19] SMTP Delivery Status Notifications 12 March 1995 11.4 Relay to Bombs.AF.MIL The SMTP at Pure-Heart.ORG relays the message to Bombs.AF.MIL, which does not support the SMTP extension. Because the sender specified NOTIFY=NEVER for recipient Fred@Bombs.AF.MIL, the SMTP at Pure-Heart.ORG chooses to send the message for that recipient in a separate transaction with a reverse-path of <>. <<< 220-Bombs.AF.MIL reporting for duty. <<< 220 Electronic mail is to be used for official business only. >>> EHLO Pure-Heart.ORG <<< 502 command not implemented >>> RSET <<< 250 reset >>> HELO Pure-Heart.ORG <<< 250 Bombs.AF.MIL >>> MAIL FROM: <<< 250 ok >>> RCPT TO: <<< 250 ok >>> DATA <<< 354 send message >>> (message goes here) >>> . <<< 250 message accepted >>> MAIL FROM:<> <<< 250 ok >>> RCPT TO: <<< 250 ok >>> DATA <<< 354 send message >>> (message goes here) >>> . <<< 250 message accepted >>> QUIT <<< 221 Bombs.AF.MIL closing connection K. Moore Expires 12 September 1995 [Page 20] SMTP Delivery Status Notifications 12 March 1995 11.5 Forward from George@Tax-ME.GOV to Sam@Boondoggle.GOV The SMTP at Pure-Heart.ORG relays the message to Tax-ME.GOV. (this step is not shown). MTA Tax-ME.GOV then forwards the message to Sam@Boondoggle.GOV (shown below). Both Tax-ME.GOV and NSA.GOV support the SMTP DSN extension. Note that RET, ENVID, and ORCPT all retain their original values. <<< 220 IRS.GOV says hello >>> EHLO Pure-Heart.ORG <<< 250-mail.Big-Bucks.COM <<< 250 DSN >>> MAIL FROM: RET=HDRS ENVID=QQ314159 <<< 250 sender okay >>> RCPT TO: NOTIFY=SUCCESS ORCPT=George@Tax-ME.GOV <<< 250 recipient okay >>> DATA <<< 354 send message >>> (message goes here) >>> . <<< 250 message received >>> QUIT <<< 221 bcnu K. Moore Expires 12 September 1995 [Page 21] SMTP Delivery Status Notifications 12 March 1995 11.6 Success DSN for Bob@Big-Bucks.COM MTA mail.Big-Bucks.COM successfully delivers the message to Bob@Big- Bucks.COM. Because the sender specified NOTIFY=SUCCESS, mail.Big- Bucks.COM issues the following DSN, and sends it to Alice@Pure- Heart.ORG. To: Alice@Pure-Heart.ORG From: postmaster@mail.Big-Bucks.COM Subject: Delivery Notification (success) for Bob@Big-Bucks.COM Content-Type: multipart/report; report-type=delivery-status; boundary=abcde MIME-Version: 1.0 --abcde Content-type: text/plain; charset=us-ascii Your message (id QQ314159) was successfully delivered to Bob@Big-Bucks.COM. --abcde Content-type: message/delivery-status Reporting-MTA: dns; mail.Big-Bucks.COM Original-Envelope-ID: QQ314159 Original-Recipient: rfc822; Bob@Big-Bucks.COM Final-Recipient: rfc822; Bob@Big-Bucks.COM Action: success Status: 2.0.0 --abcde Content-type: message/rfc822 (headers of returned message go here) --abcde-- K. Moore Expires 12 September 1995 [Page 22] SMTP Delivery Status Notifications 12 March 1995 11.7 Failed DSN for Carol@Ivory.EDU Because delivery to Carol failed and the sender specified NOTIFY=FAILURE for Carol@Ivory.EDU, MTA Pure-Heart.ORG (the SMTP client to which the failure was reported via SMTP) issues the following DSN. To: Alice@Pure-Heart.ORG From: postmaster@Pure-Heart.ORG Subject: Delivery Notification (failure) for Carol@Ivory.EDU Content-Type: multipart/report; report-type=delivery-status; boundary=bcdef MIME-Version: 1.0 --bcdef Content-type: text/plain; charset=us-ascii Your message (id QQ314159) could not be delivered to Carol@Ivory.EDU. A transcript of the session follows: (while talking to Ivory.EDU) >>> RCPT TO: NOTIFY=FAILURE <<< 550 error - no such recipient --bcdef Content-type: message/delivery-status Reporting-MTA: dns; Pure-Heart.ORG Original-Envelope-ID: QQ314159 Original-Recipient: rfc822; Carol@Ivory.EDU Final-Recipient: rfc822; Carol@Ivory.EDU SMTP-Remote-Recipient: Carol@Ivory.EDU Diagnostic-Code: smtp; 550 (error - no such recipient) Action: failed Status: 5.0.0 (error - no such recipient) --bcdef Content-type: message/rfc822 (headers of returned message go here) --bcdef-- K. Moore Expires 12 September 1995 [Page 23] SMTP Delivery Status Notifications 12 March 1995 11.8 Relayed DSN For Dana@Ivory.EDU Although the mail gateway Ivory.EDU supports the DSN SMTP extension, the LAN mail system attached to its other side does not generate positive delivery confirmations. So Ivory.EDU issues a "relayed" DSN: To: Alice@Pure-Heart.ORG From: postmaster@Ivory.EDU Subject: mail relayed for Dana@Ivory.EDU Content-Type: multipart/report; report-type=delivery-status; boundary=cdefg MIME-Version: 1.0 --cdefg Content-type: text/plain; charset=us-ascii Your message (addressed to Dana@Ivory.EDU) was successfully relayed to: ymail!Dana by the FooMail gateway at Ivory.EDU. Unfortunately, the remote mail system does not support confirmation of actual delivery. Unless delivery to ymail!Dana fails, this will be the only delivery status notification sent. --cdefg Content-type: message/delivery-status Reporting-MTA: dns; Ivory.EDU Original-Envelope-ID: QQ314159 Original-Recipient: rfc822; Dana@Ivory.EDU Final-Recipient: rfc822; Dana@Ivory.EDU Action: relayed Status: 2.0.0 --cdefg Content-type: message/rfc822 (headers of returned message go here) --cdefg-- K. Moore Expires 12 September 1995 [Page 24] SMTP Delivery Status Notifications 12 March 1995 11.9 Failure notification for Sam@Boondoggle.GOV The message originally addressed to George@Tax-ME.GOV was forwarded to Sam@Boondoggle.GOV, but the MTA for Boondoggle.GOV was unable to deliver the message due to a lack of disk space in Sam's mailbox. After trying for several days, Boondoggle.GOV returned the following DSN: To: Alice@BigHeart.ORG From: Postmaster@Boondoggle.GOV Subject: Delivery failure for Sam@Boondoggle.GOV Content-Type: multipart/report; report-type=delivery-status; boundary=defgh MIME-Version: 1.0 --defgh Your message, originally addressed to George@Tax-ME.GOV, and forwarded from there to Sam@Boondoggle.GOV could not be delivered, for the following reason: write error to mailbox, disk quota exceeded --defgh Content-type: message/delivery-status Reporting-MTA: Boondoggle.GOV Original-Envelope-ID: QQ314159 Original-Recipient: rfc822; George@Tax-ME.GOV Final-Recipient: rfc822; Sam@Boondoggle.GOV Action: failed Status: 4.2.2 (disk quota exceeded) --defgh Content-type: message/rfc822 (headers of returned message go here) --defgh-- K. Moore Expires 12 September 1995 [Page 25] SMTP Delivery Status Notifications 12 March 1995 12. References [1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, USC/Information Sciences Institute, August 1982. [2] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, UDEL, August 1982. [3] Westine, A., Postel, J. "Problems with the Maintenance of Large Mailing Lists.", RFC 1211, USC/Information Sciences Institute, March 1991. [4] Klensin, J., Freed, N., Rose, M., Stefferud, E., Crocker., D. "SMTP Service Extensions", RFC 1651, MCI, Innosoft, Dover Beach Consulting, Inc., Network Management Associates, Inc., Silicon Graphics, Inc., July 1994. [5] Moore, K., Vaudreuil, G. "An Extensible Message Format for Delivery Status Notifications", Internet-Draft draft-ietf-notary-mime- delivery-04.txt, 20 January 1995. [6] Vaudreuil, G. "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages". Internet-Draft draft-ietf- notary-mime-report-01.txt, 16 January 1995. [7] Braden, R. (ed). Requirements for Internet Hosts - Application and Support, RFC 1123, IETF, October 1989. [8] Vaudreuil, G. "Enhanced Mail System Status Codes". Internet-Draft draft-ietf-notary-status-01.txt, 24 January 1995. 13. Author's address Keith Moore University of Tennessee 107 Ayres Hall Knoxville, TN 37996-1301 USA email: moore@cs.utk.edu K. Moore Expires 12 September 1995 [Page 26]