Network Working Group                                       K. Murchison
Request for Comments: 3598                            Oceana Matrix Ltd.
Category: Standards Track                                 September 2003


             Sieve Email Filtering -- Subaddress Extension

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   On email systems that allow for "subaddressing" or "detailed
   addressing" (e.g., "ken+sieve@example.org"), it is sometimes
   desirable to make comparisons against these sub-parts of addresses.
   This document defines an extension to the Sieve mail filtering
   language that allows users to compare against the user and detail
   parts of an address.

Table of Contents

   1.  Introduction. . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Capability Identifier . . . . . . . . . . . . . . . . . . . .   2
   3.  Subaddress Comparisons. . . . . . . . . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References. . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Intellectual Property Statement . . . . . . . . . . . . . . .   5
   9.  Author's Address. . . . . . . . . . . . . . . . . . . . . . .   5
   10. Full Copyright Statement. . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Subaddressing is the practice of appending some "detail" information
   to the local-part of an [IMAIL] address to indicate that the message
   should be delivered to the mailbox specified by the "detail"
   information.  The "detail" information is prefixed with a special
   "separator character" (typically "+") which forms the boundary
   between the "user" (original local-part) and the "detail" sub-parts
   of the address, much like the "@" character forms the boundary
   between the local-part and domain.

   Typical uses of subaddressing might be:

   -  A message addressed to "ken+sieve@example.org" is delivered into a
      mailbox called "sieve" belonging to the user "ken".

   -  A message addressed to "5551212#123@example.org" is delivered to
      the voice mailbox number "123" at phone number "5551212".

   This document describes an extension to the Sieve language defined by
   [SIEVE] for comparing against the "user" and "detail" sub-parts of an
   address.

   Conventions for notations are as in [SIEVE] section 1.1, including
   use of [KEYWORDS].

2.  Capability Identifier

   The capability string associated with the extension defined in this
   document is "subaddress".

3.  Subaddress Comparisons

   Commands that act exclusively on addresses may take the optional
   tagged arguments ":user"  and ":detail" to specify what sub-part of
   the local-part of the address will be acted upon.

   NOTE: In most cases, the envelope "to" address is the preferred
   address to examine for subaddress information when the desire is to
   sort messages based on how they were addressed so as to get to a
   specific recipient.  The envelope address is, after all, the reason a
   given message is being processed by a given sieve script for a given
   user.  This is particularly true when mailing lists, aliases, and
   "virtual domains" are involved since the envelope may be the only
   source of detail information for the specific recipient.

   The ":user" argument specifies that sub-part of the local-part which
   lies to the left of the separator character (e.g., "ken" in
   "ken+sieve@example.org").  If no separator character exists, then
   ":user" specifies the entire left-side of the address (equivalent to
   ":localpart").

   The ":detail" argument specifies that sub-part of the local-part
   which lies to the right of the separator character (e.g., "sieve" in
   "ken+sieve@example.org").  If no separator character exists, the test
   evaluates to false.  If nothing lies to the right of the separator
   character, then ":detail" ":is" the null key ("").  Otherwise, the
   ":detail" sub-part contains the null key.

   Implementations MUST make sure that the separator character matches
   that which is used and/or allowed by the encompassing mail system,
   otherwise unexpected results might occur.  Implementations SHOULD
   allow the separator character to be configurable so that they may be
   used with a variety of mail systems.  Note that the mechanisms used
   to define and/or query the separator character used by the mail
   system are outside the scope of this document.

   The ":user" and ":detail" address parts are subject to the same rules
   and restrictions as the standard address parts defined in [SIEVE].
   For convenience, the "ADDRESS-PART" syntax element defined in [SIEVE]
   is augmented here as follows:

      ADDRESS-PART  =/  ":user" / ":detail"

   A diagram showing the ADDRESS-PARTs of a email address utilizing a
   separator character of '+' is shown below:

       :user "+" :detail  "@" :domain
      `-----------------'
          :local-part

   Example:

   require "subaddress";

   # File mailing list messages (subscribed as "ken+mta-filters").
   if envelope :detail "to" "mta-filters" {
     fileinto "inbox.ietf-mta-filters";
   }

   # If a message is not to me (ignoring +detail), junk it.
   if not allof (address :user ["to", "cc", "bcc"] "ken",
        address :domain ["to", "cc", "bcc"] "example.org") {
     discard;

   }

   # Redirect all mail sent to +foo.
   if envelope :detail ["to", "cc", "bcc"] "foo" {
     redirect "ken@example.edu";
   }

4.  Security Considerations

   Security considerations are discussed in [SIEVE].  It is believed
   that this extension does not introduce any additional security
   concerns.

5.  IANA Considerations

   The following template specifies the IANA registration of the Sieve
   extension specified in this document:

   To: iana@iana.org
   Subject: Registration of new Sieve extension

   Capability name: subaddress
   Capability keyword: subaddress
   Capability arguments: N/A
   Standards Track/RFC 3598
   Person and email address to contact for further information:

   Kenneth Murchison
   ken@oceana.com

   This information has been added to the list of sieve extensions given
   on http://www.iana.org/assignments/sieve-extensions.

6.  Normative References

   [IMAIL]    Resnick, P., Ed., "Internet Message Format", RFC 2822,
              April 2001.

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

   [SIEVE]    Showalter, T., "Sieve: A Mail Filtering Language", RFC
              3028, January 2001.

7.  Acknowledgments

   Thanks to Tim Showalter, Alexey Melnikov, Michael Salmon, Randall
   Gellens, Philip Guenther and Jutta Degener for their help with this
   document.

8.  Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
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   claims of rights made available for publication and any assurances of
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   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

9.  Author's Address

   Kenneth Murchison
   Oceana Matrix Ltd.
   21 Princeton Place
   Orchard Park, NY 14127

   EMail: ken@oceana.com

10.  Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

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Acknowledgement

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