Network Working Group Keith Moore Internet-Draft University of Tennessee Expires: May 20, 1995 November 20, 1994 SMTP Service Extension for Delivery Status Notifications draft-ietf-notary-smtp-drpt-02.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 and the transaction in which the 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 20 May 1995 [Page 1] SMTP Delivery Status Notifications 20 November 1994 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 or negative delivery notifications, or 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) three optional parameters are added to the RCPT command, and two optional parameters are added to the MAIL command: K. Moore Expires 20 May 1995 [Page 2] SMTP Delivery Status Notifications 20 November 1994 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 "RET", (to request that DSNs either return or not return the contents of a message), is defined in section 6.2, 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 6.3, and An optional parameter for the MAIL command, using the esmtp-keyword "OMTS", (used to specify the type of message transfer system in which the message originated), is defined in section 6.4, and 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 6.5; (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 K. Moore Expires 20 May 1995 [Page 3] SMTP Delivery Status Notifications 20 November 1994 "best effort" to ensure that such requests are honored when messages are passed into other environments. 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: 1. Multiple notify-list-elements, separated by commas, may appear in a NOTIFY parameter; however, the NEVER keyword may only appear by itself. K. Moore Expires 20 May 1995 [Page 4] SMTP Delivery Status Notifications 20 November 1994 2. Any of the keywords NEVER, SUCCESS, FAILURE, or DELAY may be spelled in any combination of upper and lower case letters. 3. Although RFC 822 ABNF syntax is used, RFC 822 style comments may not appear in NOTIFY parameter values. The meaning of the NOTIFY parameter values is generally as follows: + If the esmtp-value consists of the keyword "NEVER", a DSN should not be issued under any conditions. + If on the other hand, the esmtp-value contains one or more of the keywords "SUCCESS" or "FAILURE", a DSN should be issued on successful delivery or delivery failure, respectively. + If the esmtp-value contains the keyword "DELAY", a "delayed" DSN MAY be issued if a message cannot be delivered or relayed for an extended period of time, as determined by the MTA at which the message is delayed. The absence of the DELAY keyword in a NOTIFY parameter implies that a "delayed" DSN SHOULD NOT be issued under any conditions. 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 RET parameter of the ESMTP RCPT command The RET esmtp-keyword on the extended RCPT command specifies whether or not the message should be included in any DSN issued for this recipient. If the RET esmtp-keyword is used, it MUST have an associated esmtp-value, which should contain one of the following keywords: FULL requests that the message be returned in any delivery status notification issued for this recipient. HDRS requests that only the headers of the message not be returned. The RET parameter is optional; it need not be specified to request a DSN. If the RET parameter was not specified for a particular recipient, the MTA issuing the notification may choose to return either the entire content, or only the headers of the original message. 6.3 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. IMPORTANT: 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 K. Moore Expires 20 May 1995 [Page 5] SMTP Delivery Status Notifications 20 November 1994 conform to syntax rules for Internet addresses. Ideally, the esmtp-value associated with this parameter 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. Any valid esmtp-value (as defined in [4]) may be associated with the ORCPT keyword. However, the syntax for an esmtp-value does not allow the use of certain characters. Since such characters might appear in the original recipient address, the following scheme is used to encode the original recipient address into a valid esmtp-value: 1. Any graphic ASCII character (range 32-126 inclusive), except for "=", SP, and "%", may be encoded as itself. 2. Any octet value may be encoded using the percent character ("%") followed by two hex digits. The ORCPT parameter is optional. It should not be supplied by the SMTP client if the original recipient address (or a reasonable printable-text representation thereof) is not available to the client. 6.4 The OMTS parameter to the ESMTP MAIL command The OMTS esmtp-keywoard of the SMTP MAIL command is used to specify the "original MTS type", which identifies the type of mail system from which the message originated, and will appear in the Original-MTS-Type field in any DSNs generated for this message. The OMTS esmtp-keyword must have an associated esmtp-value. The esmtp-value associated with this parameter must be a legal MTS-type, as defined in [5]. Note: The definition of the MTS-type indicated by the OMTS esmtp- keyword may specify the syntax of recipient addresses to be used in Delivery Status Notifications. Whenever a foreign address does not consist entirely of printable ASCII characters, the definition of the sender's MTS-type (as supplied in the OMTS parameter) governs how such foreign addresses are expressed via the ORCPT parameter as well as in DSNs. The OMTS parameter is optional. It should not be supplied to an SMTP server if the original MTS-type is not known by the client. K. Moore Expires 20 May 1995 [Page 6] SMTP Delivery Status Notifications 20 November 1994 6.5 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 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. Use of the ENVID esmtp-keyword is optional. It need not be specified to request a DSN. 6.6. Restrictions on the use of Delivery Status Notification parameters No more than one each of the OMTS and ENVID parameters may appear in a 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". No more than one each of the NOTIFY, RET, and ORCPT parameters may appear in any RCPT command. If multiple occurrences of any of these parameters appear in a RCPT command, the ESMTP server should respond with "501 syntax error in parameters or arguments". 7. MTA conformance requirements 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, (in its role as an SMTP server) issues the DSN keyword in response to the EHLO command, MUST obey the rules below for a "conforming MTA" below. The terms "conforming SMTP client" and "conforming SMTP server" refer to a "conforming MTA" when acting in the role of an SMTP server or client, respectively. 7.1 ESMTP protocol interactions The following rules apply to ESMTP transactions in which any of the OMTS, ENVID, NOTIFY, RET, or ORCPT keywords are used: 1. If an SMTP client issues a MAIL command containing a valid ENVID parameter and associated esmtp-value and/or a valid OMTS parameter K. Moore Expires 20 May 1995 [Page 7] SMTP Delivery Status Notifications 20 November 1994 and associated esmtp-value, a conforming ESMTP 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 MAY NOT refuse a MAIL command based on the presence or absence of ENVID or OMTS 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 OMTS parameter in a particular MAIL command, the server should issue the response "501 syntax error in parameter". 2. If an SMTP client issues a RCPT command containing any valid NOTIFY, RET, and/or ORCPT parameters, a conforming SMTP server MUST return the same response as it would to the same RCPT command without those NOTIFY, RET, and ORCPT parameters. A conforming SMTP server MAY 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 SMTP client, when relaying a message which was received via the SMTP protocol, to an SMTP server that supports the Delivery Status Notification service extension: 1. 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, no ENVID parameter shall be supplied when the message is relayed. 2. Any OMTS 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 not OMTS parameter was included in the MAIL command when the message was received, no OMTS parameter shall be supplied when the message is relayed. K. Moore Expires 20 May 1995 [Page 8] SMTP Delivery Status Notifications 20 November 1994 3. 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 any RET or ORCPT parameters were present in the RCPT command for this recipient when the message was received, they must also appear in the RCPT command issued when relaying the message. When relaying a message to a particular recipient, no NOTIFY, RET, or ORCPT parameters may be supplied which were not present in the RCPT command for that recipient when the message was received. 7.2.2. Relay of messages to non-conforming SMTP servers The following rules govern the behavior of a conforming SMTP 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: 1. No ENVID, OMTS, NOTIFY, RET, or ORCPT parameters may be issued when relaying the message. 2. 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. 3. 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. 4. If the NOTIFY parameter was supplied for a recipient with an esmtp- value of NEVER, no DSN is issued, regardless of the reply-code returned by the SMTP server. 5. 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. 6. 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. 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: K. Moore Expires 20 May 1995 [Page 9] SMTP Delivery Status Notifications 20 November 1994 1. 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. 2. If the NOTIFY parameter was supplied for that recipient with an esmtp-value of NEVER, no DSN is issued. 3. If the NOTIFY parameter was not supplied for that recipient, no DSN is issued. 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: 1. 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. 2. 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. 3. If a NOTIFY parameter was supplied with an esmtp-keyword of NEVER, no DSN should be issued. 4. If the NOTIFY parameter was not supplied for a particular recipient, no DSN should be issued by the gateway, but the gateway should attempt to ensure that appropriate notification will be provided by the foreign mail environment if eventual delivery failure occurs. 5. When gatewaying a message into a foreign environment, the return-of- content conditions specified by any RET parameter are nonbinding; however, the MTA should attempt to honor the request using whatever mechanisms exist in the foreign environment. 7.2.5. Delays in delivery A conforming MTA which receives a message via the SMTP protocol which is unable to deliver 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: K. Moore Expires 20 May 1995 [Page 10] SMTP Delivery Status Notifications 20 November 1994 1. If the NOTIFY parameter was supplied for a recipient and its value included the DELAY keyword, a "delayed" DSN may be issued. 2. If the NOTIFY parameter was not supplied for a recipient, a "delayed" DSN may be issued. 3. If the NOTIFY parameter was supplied which did not contain the DELAY keyword, a "delayed" DSN may 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: 1. If a NOTIFY parameter was supplied for the recipient with an esmtp- keyword containing the value FAILURE, a "failed" DSN should be issued by the MTA. 2. If a NOTIFY parameter was supplied for the recipient which did not contain the value FAILURE, no DSN should be issued for that recipient. 3. If no NOTIFY parameter was supplied for the recipient, a "failure" DSN should 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: 1. Any envelope-id and original-mts-type included with the message as received, should be propagated in each ESMTP session used to forward the message to a conforming MTA. 2. Any NOTIFY, ORCPT, or RET parameters associated with a particular recipient should be propagated, for each of the recipients to which the message is forwarded. However, if the message is to be forwarded to multiple recipient addresses on behalf of a single recipient, a "delivered" DSN should be issued, and the request for a DSN should NOT be propagated to the recipient's forwarding addresses. K. Moore Expires 20 May 1995 [Page 11] SMTP Delivery Status Notifications 20 November 1994 (NOTE IN DRAFT: this is intended to ensure exactly one notification per request. I'm concerned that DSNs will be difficult to use by mailing list exploders if it's possible to get more than one notification per request, say because a message was forwarded to two recipients, and delivery succeeds for one and fails for the other. On the other hand, it's 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 should be issued. Any envelope-id, original-mts-type, notify-request, return-of-content- request, or original-recipient-address should 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 NOTIFY parameter was supplied which contained the FAILURE keyword, or no NOTIFY parameter was supplied, a "failed" DSN should be 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 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 K. Moore Expires 20 May 1995 [Page 12] SMTP Delivery Status Notifications 20 November 1994 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 empty string. The recipient address (in the RCPT command) is copied from the MAIL command of the message for which a delivery notification is being issued. The envelope of a delivery notification may not use the DSN option. 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 [6]). 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 must be "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. When generating a DSN for a message which was received via the SMTP protocol, a conforming MTA will generate the per-message fields of the multipart/delivery-status body part as follows: (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. (b) if an OMTS parameter was present on the MAIL command, an Original- MTS-Type field must be supplied, and the value associated with the OMTS parameter must appear in that field. (c) The Final-MTA field must be supplied, and it must contain the domain name of the SMTP server which is actually issuing this notification. (d) The Final-MTS-Type field must be supplied. For DSNs generated for messages received by SMTP, the Final-MTS-Type will normally be K. Moore Expires 20 May 1995 [Page 13] SMTP Delivery Status Notifications 20 November 1994 "Internet". (e) Other per-message fields as defined in [5] MAY be supplied. (f) If the ORCPT parameter was provided for this recipient, the Original-Recipient field should appear, with its value taken from the ORCPT parameter. (g) If the OMTS parameter was provided for this recipient, the Original- MTS-Type field must appear, with its value taken from the OMTS paramter. (h) For DSNs resulting from attempts to relay a message to a recipient via SMTP, the Remote-* fields must be supplied. In this case, Remote-MTS-Type will normally be "Internet". (i) Other per-recipient fields defined in [5] may also appear, as appropriate. 9. Acknowledgments (fill in this space) 10. 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-03.txt", 20 November 1994. [6] Vaudreuil, G. "Multipart/Report". Internet-Draft "draft-ietf- notary-mime-report-00.txt", 1 August 1994. K. Moore Expires 20 May 1995 [Page 14] SMTP Delivery Status Notifications 20 November 1994 11. Author's address Keith Moore University of Tennessee 107 Ayres Hall Knoxville, TN 37996-1301 USA email: moore@cs.utk.edu K. Moore Expires 20 May 1995 [Page 15] SMTP Delivery Status Notifications 20 November 1994 APPENDIX: Summary of changes since draft-ietf-notary-smtp-drpt-01.txt 1. Added OMTS esmtp-keyword to convey Original-MTS-Type. 2. Changed syntax of NOTIFY parameters to be either a comma-separated list from the set SUCCESS, FAILURE, DELAY, or the single keyword NEVER. 3. Changed syntax of RET parameter to specify either return of content or return of headers only. 4. Updated to reflect the current DSN and multipart/report drafts. 5. Updated references. K. Moore Expires 20 May 1995 [Page 16]