





                                                             A. Ward
INTERNET-DRAFT
Category:  Experimental                                 7 April 2000
draft-ward-esmtp-slide-01.txt              Exprires:  7 October 2000


             SMTP Service Extension for Slightly Differing
                       Multicast Messages (SLIDE)


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
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Abstract

   This memo defines an extension to the SMTP service [Klensin, et al
   1995] to realize efficiency improvements in the relaying and delivery
   of slightly differing messages bound for more than one recipient, as
   specified by multiple RCPT TO commands [Postel 1982].

0. Revision History

   The first version (-00) of this document was unleashed on 9 March
   2000.

   (-01)  Added section (5.1), regarding the impact of the SLIDE
   extension to signed or encrypted messages.  Modified the first
   example in section (4.) to make the impact of SLIDE more explicit.

0.0 Conventions Used in this Document



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   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 [Bradner
   1997].

1. Introduction

   SMTP is an Internet message protocol that is used to send messages to
   one or more recipients.  To realize any efficiency when sending a
   message to multiple recipients, the message body and all headers must
   be identical.  It is desirable, under some circumstances, to send
   messages to multiple recipients that differ only slightly in their
   body and/or headers.

   Under SMTP [Postel 1982] such a scenario would result in a different
   message being sent from the initial client SMTP through each relay
   server until the final server SMTP is reached.  In situations where
   more that one of the multiple recipients have mail handled by the
   same server SMTP, a significant bandwidth reduction can be realized
   with the SLIDE service extension.

2. Framework for the Slightly Differing Multicast Message Extension

   The slightly differing multicast message extension is as follows:

   (1) the name of the SMTP service extension defined here is slightly-
   differing-multicast-message;

   (2) the EHLO keyword value associated with the extension is SLIDE;

   (3) no parameter is used with the SLIDE EHLO keyword;

   (4) no additional SMTP verbs are defined by this extension

   (5) one optional parameter using the keyword SLIDERANGE is added to
   the RCPT TO command.  The value associated with this parameter is a
   comma-delimited list of octet ranges indicating which pieces of the
   overall message SHOULD be delivered to the specified recipient.  The
   syntax for the value follows, using the ABNF notation of [Crocker
   1982]:

   sliderange-value ::= octet-range *( "," octet-range )

   octet-range ::= octet-address [ "-" octet-address ]

   octet-address ::= DIGIT *(DIGIT)

   DIGIT ::= <any one of the 10 numeric characters (0 through 9)>



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   (6) the next section specifies how support for the extension affects
   the behaviour of a server and client SMTP; and,

   (7) the maximum length of a RCPT TO command line is increased by 256
   characters by the possible addition of the SLIDERANGE keyword and
   value.  Of course, since the value could conceivably be longer than
   256 characters, implementations are welcome to allot more space for
   this purpose.

3. The slightly-differing-multicast-message Service Extension

3.1 Effects on the Client SMTP

   When a client SMTP wishes to submit (using the MAIL command) messages
   with slightly different content to recipients at the same server
   SMTP, it first issues the EHLO command to the server SMTP.  If the
   server SMTP responds with code 250 to the EHLO command, and the
   response includes the EHLO keyword value SLIDE, then the server SMTP
   is indicating that it supports the extended RCPT command.  Such a
   server SMTP will accept a message containing the combined contents of
   the slightly differing messages addressed to all of the recipients
   for delivery.  The method for combining the various message bodies
   (and interpreting combined message bodies) is described in the next
   section.

   The extended RCPT command is issued by a client SMTP when it wishes
   to transmit part of a combined message body to the specified
   recipient.  The syntax for this command is identical to the RCPT
   command in [Postel 1982], except that a SLIDERANGE parameter must
   appear after the address.  Multiple SLIDERANGE parameters may be used
   in a single RCPT command; however, in such a case, the values of the
   several parameters SHOULD be combined into a single, continuous,
   comma-delimited list of octet ranges.

   The value associated with the SLIDERANGE parameter lists which octets
   in the impending DATA command are to be sent to the specified
   recipient.

3.2 Effects on the Server SMTP

   A server SMTP which supports the slightly differing multicast message
   service extension SHOULD relay only those octets bound for recipients
   at a particular domain to the mail exchange for that domain.  If this
   suggested message trimming occurs, the octets specified in the
   SLIDERANGE parameter for each recipient MUST be adjusted to
   correspond with the changes to the message DATA.

   The final 5 octets of the message DATA (<CR><LF>.<CR><LF>) MUST



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   always be relayed, even if not explicitly specified in the SLIDERANGE
   parameter value.

   Once a server SMTP supporting the slightly differing multicast
   message service extension accepts a message for which any recipient
   has a non-trivial SLIDERANGE parameter value, the server SMTP MUST
   deliver or relay the message in such a way as to ensure that only the
   octets specified for a particular recipient will be received by that
   recipient.  As well, when the server SMTP is relaying the message, it
   SHOULD attempt to minimize the number of octets that are relayed to
   each downstream server SMTP.

4. Usage Examples

   The following dialogue illustrates the use of the slightly differing
   multicast message service extension:

   S: <wait for connection>
   C: <open connection to server>
   S: 220 anstruther.elsewhere.com SMTP ready
   C: EHLO burleigh.uwaterloo.ca
   S: 250-hello burleigh.uwaterloo.ca
   S: 250 SLIDE
   C: MAIL FROM:<andrew@burleigh.uwaterloo.ca>
   S: 250 <andrew@burleigh.uwaterloo.ca>... sender okay
   C: RCPT TO:<ed@elsewhere.com> SLIDERANGE=0-148,180-322
   S: 250 <ed@elsewhere.com>... recipient and SLIDERANGE okay
   C: RCPT TO:<doug@elsewhere.com> SLIDERANGE=0-121,149-272,320-322
   S: 250 <doug@elsewhere.com>... recipient and SLIDERANGE okay
   C: DATA
   S: 354 any octets beyond 1235 will not be relayed, end with CRLF.CRLF
   C: Message-ID: <1234.abcd@uwaterloo.ca>
   C: Date: Mon, 03 Apr 2000 12:05:10 -0400
   C: From: Andrew <andrew@burleigh.uwaterloo.ca>
   C: To: Ed <ed@elsewhere.com>
   C: To: Doug <doug@elsewhere.com>
   C: Subject: special message
   C:
   C: this is the message body for a special message
   C:
   C: enjoy, andrew
   C:
   C: ps. this is a secret that Doug doesn't know
   C: .
   S: 250 okay
   C: QUIT
   S: 250 bye bye




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   This transaction would result in ed@elsewhere.com receiving the
   message:

   Message-ID: <1234.abcd@uwaterloo.ca>
   Date: Mon, 03 Apr 2000 12:05:10 -0400
   From: Andrew <andrew@burleigh.uwaterloo.ca>
   To: Ed <ed@elsewhere.com>
   Subject: special message

   this is the message body for a special message

   enjoy, andrew

   ps. this is a secret that Doug doesn't know

   while doug@elsewhere.com whould receive:

   Message-ID: <1234.abcd@uwaterloo.ca>
   Date: Mon, 03 Apr 2000 12:05:10 -0400
   From: Andrew <andrew@burleigh.uwaterloo.ca>
   To: Doug <doug@elsewhere.com>
   Subject: special message

   this is the message body for a special message

   enjoy, andrew

   The following dialogue illustrates the efficiencies that can be
   realized in a relaying scenario:

   S1: 220 one.there.com SMTP ready
   C0: EHLO zero.here.com
   S1: 250-hello zero.here.com
   S1: 250 SLIDE
   C0: MAIL FROM:<me@here.com>
   S1: 250 <me@here.com>... sender okay
   C0: RCPT TO:<ed@everywhere.com> SLIDERANGE=0-150,200-250
   S1: 250 <ed@everywhere.com>... recipient and SLIDERANGE okay
   C0: RCPT TO:<doug@everywhere.com> SLIDERANGE=0-199
   S1: 250 <doug@everywhere.com>... recipient and SLIDERANGE okay
   C0: RCPT TO:<laurene@everywhere.com> SLIDERANGE=0-250
   S1: 250 <laurene@everywhere.com>... recipient and SLIDERANGE okay
   C0: RCPT TO:<rachael@elsewhere.com>
   S1: 250 <rachael@elsewhere.com>... recipient okay
   C0: DATA
   S1: 354 okay, send message body, end with CRLF.CRLF
   C0: ...<1000 octets of message>...
   C0: .



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   S1: 250 okay
   C0: QUIT
   S1: 250 bye bye
    ...
   S2: 220 two.everywhere.com SMTP ready
   C1: EHLO one.there.com
   S2: 250-hello one.there.com
   S2: 250 SLIDE
   C1: MAIL FROM:<me@here.com>
   S2: 250 <me@here.com>... sender okay
   C1: RCPT TO:<ed@everywhere.com> SLIDERANGE=0-150,200-250
   S2: 250 <ed@everywhere.com>... recipient and SLIDERANGE okay
   C1: RCPT TO:<doug@everywhere.com> SLIDERANGE=0-199
   S2: 250 <doug@everywhere.com>... recipient and SLIDERANGE okay
   C1: RCPT TO:<laurene@everywhere.com>
   S2: 250 <laurene@everywhere.com>... recipient okay
   C1: DATA
   S2: 354 okay, send message body, end with CRLF.CRLF
   C1: ...<octets 0 to 250 of message>...
   C1: .
   S2: 250 okay
   C1: QUIT
   S2: 250 bye bye
    ...
   S3: 220 three.elsewhere.com SMTP ready
   C1: EHLO one.there.com
   S3: 250-hello one.there.com
   S3: 250 SLIDE
   C1: MAIL FROM:<me@here.com>
   S3: 250 <me@here.com>... sender okay
   C1: RCPT TO:<rachael@elsewhere.com>
   S3: 250 <rachael@elsewhere.com>... recipient okay
   C1: DATA
   S3: 354 okay, send message body, end with CRLF.CRLF
   C1: ...<all octets of message>...
   C1: .
   S3: 250 okay
   C1: QUIT
   S3: 250 bye bye

5. Security Considerations

   This extension takes some of the "final control" over the message
   body out of the hands of the client, and places it on the server
   SMTPs that are charged with relaying and delivering the message.
   While any server SMTP has access to change the content of a message
   that it relays or delivers, a server SMTP that supports the slightly
   differing multicast message service extension is obliged to be able



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   to alter a message that takes advantage of this extension.  As a
   result of the increased handling by the server SMTP, there is more
   room for error in the message transmission.

5.1 Impact on Signed and Encrypted Messages

   Messages that are transferred between a client SMTP and a server SMTP
   over a secure channel such as SSL or TLS should not be adversely
   affected by the SLIDE extension.

   Things get messy when it comes to signing or encrypting the message
   data (all or part of the information sent to the server SMTP
   following a 354 response to the DATA command).  Two alternatives are
   suggested in section (5.1.1) and section (5.1.2).  A client SMTP may
   implement either method, as both methods can be used transparently to
   all other nodes in the chain of relays (including the final server
   SMTP node).

5.1.1 Piecewise Signing and Encryption

   With this method, the initial client SMTP may sign or encrypt each
   separate range of bytes (or part thereof), as defined by the various
   SLIDERANGE values.

   (example to follow)

5.1.2 Component Message Signing

   This method creates a single signature for each distinct message
   contained in a set of messages encoded using the SLIDE extension.
   During encoding of the SLIDE message, each component message that
   needs to be signed can have a signature generated for it before the
   component messages are SLIDE encoded.

   (example to follow)

6. Acknowledgements

   Thanks to Ed, Doug, Laurene and Rachael for their (unwilling)
   participation in the usage examples.  Thanks to Dan Wing for his
   suggested improvements in usage examples and security considerations.

7. References

   [Bradner 1997]  Bradner, S.  "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119.  March 1997.

   [Crocker 1982]  Crocker, D.  "Standard for the Format of ARPA



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   Internet Text Messages", STD 11, RFC 822.  UDEL, August 1982.

   [Klensin, et al 1995]  Klensin, J., N. Freed, M. Rose, E. Stefferud,
   and D. Crocker.  "SMTP Service Extensions", STD 10, RFC 1869.
   November 1995.

   [Postel 1982]  Postel, J.  "Simple Mail Transfer Protocol", STD 10,
   RFC 821.  USC/Information Sciences Institute, August 1982.

8. Author's Address

   Andrew Ward
   70 Gruhn Street
   Kitchener, ON  N2G 1S6
   CANADA

   Phone:  +1 519 581 1201
   EMail:  amward@uwaterloo.ca



                         EXPIRES:  7 October 2000





























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