HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 02:23:27 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Fri, 21 Nov 1997 17:00:00 GMT ETag: "2ed9b2-72c1-3475be10" Accept-Ranges: bytes Content-Length: 29377 Connection: close Content-Type: text/plain Application Area Neil Joffe Internet Draft Dan Wing November 19, 1997 Cisco Systems Expires May 1998 Larry Masinter draft-ietf-fax-smtp-session-01.txt Xerox Corporation SMTP Service Extension for Immediate Delivery 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 inappropriate 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), ftp.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). NOTE: although this work has been discussed in the IETF-FAX working group, it does not purport to represent the consensus of the group. Copyright Notice Copyright (C) The Internet Society 1997. All Rights Reserved. 0. Administrivia 0.1. Open design issues 0.1.1. Server's response to STAT The authors feel that message/delivery-status allows for all sorts of delivery information to be conveyed, including necessary Wing, Joffe, Masinter Expires April 1998 [Page 1] Internet Draft SMTP Immediate Delivery November 1997 transformations which might be necessary for some deliveries, such as fax. It was suggested to us in private email to expand this to be multipart/report, which allows non-parsable data to be sent to the SMTP client. As the examples below show, this data can be a audio or a fax (tiff-f) image. However, this may be too unwieldy for many uses of Session. Another idea is a one-line response that indicates Session delivery status as in-progress or completed, which makes combining responses easier as well. 0.1.2. STAT for each recipient or all recipients The authors have been asked to create a single command to query delivery status for all recipients (instead of requiring a separate STAT command for each recipient, as this memo is currently written). If we use DSNs, this is not possible unless we send multiple multipart/reports (or multiple message/delivery-status) because DSNs aren't designed to be coalesced. 0.2. Notes and unresolved issues More verbage needed for security section Add example showing DSN (NOTIFY=blah) in conjunction with SESSION 0.3. Changes since previous versions Changes from draft-ietf-fax-smtp-session-00.txt to -01: * Added copyright notice * Reference to [FAX-DSN]. Changes from draft-wing-smtp-session-00 to draft-ietf-fax-smtp- session-00.txt: * Server's reply to STAT is now a complete multipart/report * Language clarifications * Require immediate SMTP server reply after client sends "." Wing, Joffe, Masinter Expires April 1998 [Page 2] Internet Draft SMTP Immediate Delivery November 1997 * Specify SMTP server must respond to STAT within 30 seconds 1. Abstract This memo defines an extension to SMTP which provides a mechanism for requesting and verifying immediate message delivery over SMTP. 2. Introduction Historically, SMTP [SMTP] has been used for store and forward delivery of messages. This memo describes a new SMTP extension called SESSION. This new extension allows an SMTP client to request immediate delivery by the SMTP server. The SESSION extension allows for immediate delivery of mail; it presumes either a direct connection between sender and recipient or a chain of session-enabled servers in which each supports the SESSION extension. If an MTA in the SMTP "path" does not support SESSION, delivery automatically falls back to normal store and forward, and such fallback is communicated to the SMTP client, as described in section 4.1. Unlike the deprecated SAML, SOML and SEND commands (documented in [SMTP] and deprecated in [DRUMS]) the SESSION extension allows for a mix of immediate and store & forward delivery recipients. The SESSION extension was motivated by an analysis of the requirements for using the Internet to deliver fax messages, and, coupled with a mechanism for exchanging capabilities and preferences of sender and recipient, can be used by email<->fax gateway applications. In addition, the SESSION extension may be useful for other messaging applications where immediate delivery and confirmation are requested. This memo uses the mechanism described in [SMTP-EXT] to define an extension to the SMTP protocol for immediate delivery. 2.1. Discussion of this draft This draft is being discussed on the "ietf-fax" mailing list. To subscribe, send a message to with the line "subscribe" in the body of the message. Archives are available from http://www.imc.org/ietf-fax. Wing, Joffe, Masinter Expires April 1998 [Page 3] Internet Draft SMTP Immediate Delivery November 1997 2.2. Conventions used in this document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. If such lines are wrapped without a new "C:" or "S:" label, then the wrapping is for editorial clarity and is not part of the command. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [REQ]. 3. Framework for immediate delivery support The immediate message delivery is defined as follows: (1) The name of the immediate extension is Session; (2) the EHLO keyword value associated with the immediate extension is SESSION; (3) no parameter is used with the SESSION EHLO keyword; (4) one new SMTP verb, STAT (used to retreive an in-line DSN), is defined with this extension, and is described in section 6; (5) one optional parameter is added to the RCPT command, using the esmtp-keyword SESSION, and is described in section 5, no parameters are added to the MAIL FROM command; (6) the maximum length of a RCPT TO is increased by 8 characters. 4. Esmtp-keyword SESSION Upon receiving a RCPT command with the esmtp-keyword SESSION, a session-enabled server will normally send either a positive (2xx) or negative (5xx) reply to the SMTP client. A 250 reply code indicates that the session-enabled server believes the message will be sent immediately -- that is, that the request for SESSION delivery will be honored. Note that SESSION delivery can subsequently fail due to disk space exhaustion, disk quotas, failure of a remote MTA, loss of connectivity to a remote MTA, or other reasons. The MTA that detected the failure may attempt to deliver the message via store-and-forward -- the SMTP client may use the STAT command to determine the delivery status of the message. Wing, Joffe, Masinter Expires April 1998 [Page 4] Internet Draft SMTP Immediate Delivery November 1997 If a session-enabled server is unable to send a message immediately (that is, the request for SESSION will not be honored), but the session-enabled server is willing to send the message via store-and- forward, it MUST respond with a 252 reply code. The SMTP client can use this information to inform the user that immediate delivery isn't available, and the SMTP client (or the user) may decide to abort the SMTP transaction. 5. New SMTP verb STAT One new SMTP verb is introduced with the Session extension. The STAT verb allows a client to query the session delivery status for all recipients in this mail transaction. The STAT command, and the server's reply to STAT, are sent along the SMTP "path". Using the diagram in section 4, the SMTP client (A) would send a STAT command to (B), and (B) would forward the STAT command to (C), which forwards it to (D). (D) generates the reply to STAT which is echoed back through the MTAs until it is finally sent by (B) to (A). The syntax of the STAT verb, using the notation described in [ABNF], is: stat-cmd = "STAT" SP CR LF The reply to the STAT command is called an ``in-line Delivery Status Notification'', or ``in-line DSN''. The SMTP server MUST respond to a STAT command no later than 60 seconds after a STAT command is received. After 120 seconds an SMTP client MAY assume the connection to the SMTP server is broken. 5.1. Format of in-line Delivery Status Notification The reply to STAT is a multipart/report as defined in [MIME-RPT]. However, note that this Session extension does NOT require the session-enabled SMTP server also implement Delivery Status Notifications [SMTP-DSN]. Each line of the multipart/report is sent following the rules for SMTP replies. In the notation described in [ABNF]: inline-dsn = *( "250-" [status-code SP] dsn-line CR LF ) "250 " [status-code SP] dsn-line CR LF Wing, Joffe, Masinter Expires April 1998 [Page 5] Internet Draft SMTP Immediate Delivery November 1997 dsn-line = status-code = of section 4 of [SMTP- ENH-ERR] if SMTP server implements [SMTP-ENH- ERR]> text = Note that the information returned can include extension fields, such as those defined in [FAX-DSN]. 5.2. Per-recipient DSN extension [DSN] permits extension fields to be defined. The following new per-recipient DSN extension is defined for each recipient that had the esmtp-keyword SESSION. In the notation described in [ABNF]: extension-field = "Session-Delivery" *WSP ":" *WSP session-status session-status = "delivered" / "in-progress" / "queued" The and can be spelled in any combination of uppercase and lowercase letters. "delivered" Session delivery was successful. Message was delivered to the recipient immediately. This is a terminal value. "in-progress" Session delivery has not yet completed. A STAT command issued later will show final status of this message. This is the only non-terminal value. "queued" Session delivery failed for some reason, but the MTA was able to successfully queue the message using normal SMTP store-and-forward. One cause of this status is when the session-enabled server forwards the message to a non-session-enabled server. This is a terminal value. Once a terminal value in-line DSN has been sent for a specific forward-path, the SMTP server does not need to include that forward- path in subsequent STAT replies. If an SMTP client sends a STAT command and the SMTP server has already informed the SMTP client that all recipients had a terminal values, the SMTP server should return a 503 reply. Wing, Joffe, Masinter Expires April 1998 [Page 6] Internet Draft SMTP Immediate Delivery November 1997 5.3. Delivery notifications and STAT During normal store and forward operation and in the absence of special RFC822 headers (such as Return-Receipt-To, Generate- Delivery-Report described in [HEADERS]), only a delivery failure causes a message to be generated (commonly called a `bounce'). If an SMTP server implments [SMTP-DSN], the SMTP client may request a delivery status notification, and such a request may be for actions other than delivery failure (such as SUCCESS or DELAY). XXX A session-enabled server SHOULD NOT send such a `bounce' (or DSN) message if the recipient included the esmtp-keyword SESSION, and the SMTP server can be positive that the SMTP client has already received the same information from the in-line delivery status notification. For example, if the SMTP client sends a QUIT command after the SMTP server has sent the in-line delivery status notification, the SMTP server knows the SMTP client has successfully received the in-line delivery status notification. XXX - bzzt: pipelining allows the "." and QUIT commands to be sent at the same time. How should we resolve this problem? If the RCPT command included the esmtp-keyword SESSION, any DSN generated must include the DSN per-recipient extension defined in section 5.2 -- omission of this extension implies "Session-Delivery: queued" (because the message was sent through an MTA that doesn't support SESSION). 5.4. Usage of [DSN] fields For Session recipients, the , described in [DSN], can be used to indicate when the SMTP server will stop attempting to deliver the Session message. Note it is not possible to determine if the Delivery-Status will be "queued" or "delivered" except by querying via another STAT command. XXX - Is this going to be sufficient for our FAX needs? We could add more things, like bytes, pages, seconds-to-completion for in- progress. Would another extension be useful to indicate how long it took to send the fax (for billing)? 6. Behavior with multiple hop delivery Both the esmtp-keyword SESSION and the new SMTP verb STAT require Wing, Joffe, Masinter Expires April 1998 [Page 7] Internet Draft SMTP Immediate Delivery November 1997 special behavior when dealing with multiple-hop delivery. Multiple- hop delivery occurs when the sending mailer isn't communicating directly with the receiving mailer -- that is, there are intervening mail transfer agents (MTAs) between the sending mailer and the receiving mailer. 6.1. esmtp-keyword SESSION The following sections describe the behavior of the SMTP server when a RCPT command contains the esmtp-keyword SESSION. 6.1.1. SESSION local delivery In the case of a local delivery, the SESSION keyword causes the session-enabled server to attempt immediate delivery of the message to the local user's mailbox. 6.1.2. SESSION relayed delivery The following diagram is used to help describe the relayed delivery behavior. The diagram depicts a user agent sending mail to two recipients with the esmtp-keyword SESSION, and each recipient has a different MTA. +-------+ +-----------+ -=> | MTA-1 | => | receiving | user@host-x / | | | MTA-1 | +-----+ +--------+ / +-------+ +-----------+ | user| => |Original| =< (C) (D) |agent| | MTA | \ +-----+ +--------+ \ +-------+ +-----------+ (A) (B) -=> | MTA-2 | => | receiving | user@host-y | | | MTA-2 | +-------+ +-----------+ (E) (F) In the case of several MTAs in the SMTP 'path', as in the above diagram, the RCPT command with the esmtp-keyword SESSION is forwarded to the next MTA (before the current MTA responds to the RCPT command) until finally the RCPT command is sent to the 'last' MTA which actually sends a reply. The reply is then echoed back along the SMTP 'path'. Thus in the above diagram, if (A) issued two RCPT commands, the order of processing is as follows: Wing, Joffe, Masinter Expires April 1998 [Page 8] Internet Draft SMTP Immediate Delivery November 1997 (1) A>B: ... normal SMTP initiation sequence... (2) A>B: RCPT TO: SESSION (3) B>C: ... normal SMTP initiation sequence... (4) B>C: RCPT TO: SESSION (5) C>D: ... normal SMTP initiation sequence... (6) C>D: RCPT TO: SESSION (7) D>C: 220 okay (8) C>B: 220 okay (9) B>A: 220 okay (10) A>B: RCPT TO: SESSION (11) B>E: ... normal SMTP initiation sequence... (12) B>E: RCPT TO: SESSION (13) E>F: ... normal SMTP initiation sequence... (14) E>F: RCPT TO: SESSION (15) F>E: 220 okay (16) E>B: 220 okay (17) B>A: 220 okay The DATA command is also handled in a parallel function, such that a single DATA command from (A) is transmitted to (B), which then sends a DATA command to both (C) and (E). During mail data transfer, each MTA is expected to stream the network data to the next MTA (or to the local user's mailbox, as appropriate) -- that is, the data should be sent from the MTA while it is being received. When (B) receives the end-of-mail indicator, it must reply to (A) as soon as possible to prevent duplicate messages as described in [DUPLICATE]. The MTA at (C) and (D) must likewise reply to the end-of-mail indicator as soon as possible. 6.1.3. Excessive delays with multiple MTAs The cumulative delays of going through many MTAs will cause Session delivery to fail (by falling back to normal store-and-forward). Proper configuration and deployment of SMTP servers will prevent this problem. Implementors must carefully design session-enabled MTAs to respond quickly when Session recipients are present to minimize timing problems. 7. Implementation notes Wing, Joffe, Masinter Expires April 1998 [Page 9] Internet Draft SMTP Immediate Delivery November 1997 7.1. SMTP server reply to STAT To prevent excessive network activity by an SMTP client querying delivery status "too often", the SMTP server may delay responding to a client's STAT command. Such a delay MUST NOT exceed 10 seconds. 7.2. PIPELINING implementation recommendation Due to the delays inherent with establishing connections with each MTA in the SMTP "path", SMTP servers that implement this SESSION extension SHOULD also implement [SMTP-PIPE]. This permits the SMTP client to send the STAT command immediately after the end-of-mail- data indicator, without waiting for the SMTP server's reply to the end-of-mail-data indicator. 8. Security Considerations Denial of service attacks are possible with SESSION. XXX - more verbage 9. Examples 9.1. Successful Session delivery to two recipients This example shows a successful Session delivery with two recipients. The first recipient, masinter@parc.xerox.com, was still being queued when the first STAT command was sent by the client, but a subsequent STAT command shows the final status. Note also that the in-line DSN for njoffe@cisco.com includes a both a TIFF (fax format) and audio reply, which may be used directly by some mail user agents. This is merely an example to show how in-line DSNs might be useful for low-end SMTP clients; a good SMTP server implementation would only special content-types if it had reason to believe the SMTP client could use them. S: 220 mailer.cisco.com ESMTP service ready C: EHLO pc.cisco.com S: 250-mailer.cisco.com says hello S: 250 SESSION C: MAIL FROM: S: 250 Sender ok C: RCPT TO: SESSION Wing, Joffe, Masinter Expires April 1998 [Page 10] Internet Draft SMTP Immediate Delivery November 1997 S: 250 and options ok C: RCPT TO: SESSION S: 250 and options ok C: DATA S: 354 Enter your data C: From: Dan Wing C: To: njoffe@cisco.com, masinter@parc.xerox.com C: Date: Mon, 6 Oct 1997 12:42:32 -0700 C: Subject: Palo Alto Coffee shops C: C: Please let me know your favorite coffee shop in Palo Alto. C: . S: 250 message accepted C: STAT S: 250-Content-type: multipart/report;boundary="MessageBoundary" S: 250- S: 250---MessageBoundary S: 250-Content-type: text/plain S: 250- S: 250-Your message is still being sent to: S: 250- S: 250-Recipient address: masinter@parc.xerox.com S: 250-Reason: Still writing 32 bytes to remote system S: 250- S: 250---MessageBoundary S: 250-Content-type: message/delivery-status S: 250- S: 250-Original-envelope-id: 01IOHGLWJLHE8X2IDT@Cisco.COM S: 250-Reporting-MTA: dns; parc-1.xerox.com S: 250- S: 250-Action: delivered S: 250-Status: 2.0.0 S: 250-Final-recipient: rfc822;masinter S: 250-Session-Delivery: in-progress S: 250- S: 250 --MessageBoundary-- C: STAT S: 250-Content-type: multipart/report;boundary="MessageBoundary" S: 250- S: 250---MessageBoundary S: 250-Content-type: multipart/alternative;boundary="AltBoundary" S: 250- S: 250---AltBoundary S: 250-Content-type: text/plain S: 250- S: 250-Your message was successfully delivered to these recipients: S: 250- S: 250-Recipient address: njoffe@cisco.com Wing, Joffe, Masinter Expires April 1998 [Page 11] Internet Draft SMTP Immediate Delivery November 1997 S: 250-Reason: Successfully delivered immediately to local user. S: 250- S: 250---AltBoundary S: 250-Content-type: audio/basic S: 250-Content-Transfer-Encoding: base64 S: 250- S: 250-ABCDEF01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF S: 250-ABCDEF01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF S: 250-ABCDEF01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF S: 250- S: 250---AltBoundary S: 250-Content-type: tiff; application=f S: 250-Content-Transfer-Encoding: base64 S: 250- S: 250-01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF012345 S: 250-01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF012345 S: 250-01234567890ABCDEF01234567890ABCDEF01234567890ABCDEF012345 S: 250- S: 250---AltBoundary-- S: 250- S: 250---MessageBoundary S: 250-Content-type: message/delivery-status S: 250- S: 250-Original-envelope-id: 01IOHGLWJLHE8X2IDT@Cisco.COM S: 250-Reporting-MTA: dns; lint.cisco.com S: 250- S: 250-Action: delivered S: 250-Status: 2.0.0 (Delivered immediately to local user) S: 250-Final-recipient: rfc822;njoffe S: 250-Session-Delivery: delivered S: 250- S: 250 --MessageBoundary-- C: STAT S: 250-Content-type: MULTIPART/REPORT;BOUNDARY="MessageBoundary" S: 250- S: 250---MessageBoundary S: 250-Content-type: text/plain S: 250- S: 250-Your message was successfully delivered to these recipients: S: 250- S: 250-Recipient address: masinter@parc.xerox.com S: 250-Reason: Successfully delivered immediately to local user. S: 250- S: 250---MessageBoundary S: 250-Content-type: message/delivery-status S: 250- S: 250-Original-envelope-id: 01IOHGLWJLHE8X2IDT@Cisco.COM S: 250-Reporting-MTA: dns; parc-1.xerox.com Wing, Joffe, Masinter Expires April 1998 [Page 12] Internet Draft SMTP Immediate Delivery November 1997 S: 250- S: 250-Action: delivered S: 250-Status: 2.0.0 S: 250-Final-recipient: rfc822;masinter S: 250-Session-Delivery: delivered S: 250- S: 250 --MessageBoundary-- C: QUIT S: 221 Goodbye 9.2 XXX - other examples? 10. Acknowledgments Much of this document was produced by work begun in the Internet FAX Working Group of the IETF. The authors would like to thank Graham Klyne (Integralis Ltd.) for his contributions to this work. 11. References [ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [CHUNKING] G. Vaudreuil, "SMTP Service Extensions for Transmission of Large and Binary MIME Messages", RFC 1830 (Experimental), August 1995. [DSN] K. Moore, G. Vaudreuil, "An Extensible Message Format for Delivery Status Notifications", RFC 1894, January 1996. [DRUMS] J. Klensin, D. Mann, "Simple Mail Transfer Protocol", Internet Draft, Work in Progress, draft-ietf-drums-smtpupd- ??.txt. [DUPLICATE] C. Partridge, "DUPLICATE MESSAGES AND SMTP", RFC 1047, February 1988. [FAX-DSN] D. Wing, "Extensions to Delivery Status Notifications for Fax", Internet Draft, Work in Progress, draft-ietf-fax-dsn- extensions-??.txt. [HEADERS] J. Palme, "Common Internet Message Headers", RFC 2076, February 1997. Wing, Joffe, Masinter Expires April 1998 [Page 13] Internet Draft SMTP Immediate Delivery November 1997 [MIME-RPT] G. Vaudreuil, "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892, January 1996. [REQ] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP-14, RFC 2119, March 1997. [SMTP] J. Postel, "Simple Mail Transfer Protocol", STD-10, RFC 821, August 1982. [SMTP-DSN] K. Moore, "SMTP Service Extension for Delivery Status Notifications", RFC 1891, January 1996. [SMTP-ENH-ERR] N. Freed, "SMTP Service Extension for Returning Enhanced Error Codes", RFC 2034, October 1996. [SMTP-EXT] J. Klensin, N. Freed, M. Rose, E. Stefferud, D. Crocker, "SMTP Service Extensions", STD-10, RFC 1869, November 1995. [SMTP-PIPE] N. Freed, "SMTP Service Extension for Command Pipelining", RFC 2197, September 1997. 12. Copyright Copyright (C) The Internet Society 1997. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Wing, Joffe, Masinter Expires April 1998 [Page 14] Internet Draft SMTP Immediate Delivery November 1997 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 13. Authors' Addresses Dan Wing Cisco Systems, Inc. 101 Cooper Street Santa Cruz, CA 95060 USA Phone: +1 408 457 5200 Fax: +1 408 457 5208 EMail: dwing@cisco.com Neil Joffe Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA Phone: +1 408 526 4000 Email: njoffe@cisco.com Larry Masinter Xerox Palo Alto Research Center 3333 Coyote Hill Road Palo Alto, CA 94304 USA Phone: +1 415 812 4365 Fax: +1 415 812 4333 EMail: masinter@parc.xerox.com Wing, Joffe, Masinter Expires April 1998 [Page 15]