Sieve Working Group                                         K. Murchison
Internet-Draft                                Carnegie Mellon University
Obsoletes: 3598 (if approved)                          February 15,                             April 18, 2006
Expires: August 19, October 20, 2006

             Sieve Email Filtering -- Subaddress Extension
                   draft-ietf-sieve-rfc3598bis-02.txt
                     draft-ietf-sieve-rfc3598bis-03

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Copyright Notice

   Copyright (C) The Internet Society (2006).

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
   sub-parts of an address.

Meta-information on this document
   This information is intended to facilitate discussion.  It will be
   removed when this document leaves the Internet-Draft stage.

   This document is intended to be an update to the existing
   "subaddress" extension to the Sieve mail filtering language,
   available from the RFC repository as
   <ftp://ftp.isi.edu/in-notes/rfc3598.txt> and
   <ftp://ftp.isi.edu/internet-drafts/draft-ietf-sieve-3028bis-05.txt>
   <ftp://ftp.isi.edu/internet-drafts/draft-ietf-sieve-3028bis-06.txt>
   respectively.

   This document and the Sieve language itself are being discussed on
   the MTA Filters mailing list at <mailto:ietf-mta-filters@imc.org>.
   Subscription requests can be sent to
   <mailto:ietf-mta-filters-request@imc.org?body=subscribe> (send an
   email message with the word "subscribe" in the body).  More
   information on the mailing list along with an archive of back
   messages is available at <http://www.imc.org/ietf-mta-filters/>.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions used in this document  . . . . . . . . . . . . . .  5
   3.  Capability Identifier  . . . . . . . . . . . . . . . . . . . .  5
   3.  6
   4.  Subaddress Comparisons . . . . . . . . . . . . . . . . . . . .  6
   4.  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   5.
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 11
   Appendix B.  Changes since RFC3598 . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 14

1.  Introduction

   Subaddressing is the practice of augmenting (usually with a suffix) the local-part of an
   [RFC2822] address with some "detail" information to indicate that the
   message should be delivered to the mailbox specified by the "detail"
   information.  A  One common way of encoding "detail" information into
   the local-part is to add a "separator character
   sequence" (typically "+"), forms the sequence", such as
   "+", to form a boundary between the "user" (original local-part) and
   "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:

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

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

   This document describes an extension to the Sieve language defined by
   [I-D.ietf-sieve-3028bis] for comparing against the "user" and
   "detail" sub-parts of an address.

2.  Conventions used in this document

   Conventions for notations are as in [I-D.ietf-sieve-3028bis] section
   1.1, including use of
   1.1.

   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 [RFC2119].

2.

3.  Capability Identifier

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

3.

4.  Subaddress Comparisons

   Commands

   Test 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.

      NOTE: Because the construction encoding of detailed addresses can be are site and/or
      implementation specific, using the subaddress extension on foreign
      addresses (such as the envelope "from" address or originator
      header fields) may lead to inconsistent or incorrect results.

   The ":user" argument specifies the user sub-part of the local-part of
   an address.  The positioning of the user sub-part with respect to  If the
   separator character sequence address is dependent on the encompassing mail
   system.  If no separator character sequence exists, not encoded to contain a detail sub-
   part, then ":user" specifies the entire left-side of the address
   (equivalent to ":localpart").

   The ":detail" argument specifies the detail sub-part of the local-
   part of an address.  The positioning of the detail sub-part with
   respect to  If the separator character sequence address is dependent on the
   encompassing mail system.  If no separator character sequence exists, not encoded to contain a
   detail sub-part, then the test evaluates to false.  If a zero-length
   string is encoded as the separator character sequence
   exists, but no detail information is provided, sub-part, then ":detail" ":is" the
   empty key ("").  Otherwise, the ":detail" sub-part ":contains"
   the empty key.

      NOTE: If the encoding method used for detailed addresses utilizes
      a separator character sequence, and the separator character
      sequence occurs more than once in the local-part, then the logic
      used to split the address is implementation defined, and is
      usually dependent on the format used by the encompassing mail
      system.

   Implementations MUST make sure that the separator character sequence
   and the ordering of the user and detail sub-parts match those encoding method used for
   detailed addresses matches that
   are which is used and/or allowed by the
   encompassing mail system, otherwise unexpected results might occur.  Implementations SHOULD allow the
   separator character sequence and sub-part ordering 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
   sequence and sub-part ordering encoding
   method 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 [I-D.ietf-
   sieve-3028bis].
   sieve-3028bis] Section 2.7.4.

   For convenience, the "ADDRESS-PART" syntax element defined in
   [I-D.ietf-sieve-3028bis] Section 2.7.4 is augmented here as follows:

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

   A diagram showing the ADDRESS-PARTs of a email address where the
   detail information follows a separator character sequence of "+" is
   shown below:

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

   A diagram showing the ADDRESS-PARTs of a email address where the
   detail information precedes a separator character sequence of "--" is
   shown below:

          :detail "--" :user  "@" :domain
         `------------------'
         \------------------/
             :local-part

   Example (where the detail information follows "+"):

      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 directly to me (ignoring +detail), junk it.
      if not allof (address :user ["to", "cc"] "ken",
                    address :domain ["to", "cc"] "example.org") {
          discard;
      }

      # Redirect all mail sent to +foo.
      if envelope :detail "to" "foo" {
          redirect "ken@example.edu"; "ken@example.net";
      }

4.

5.  IANA Considerations

   This document requests that the IANA update the entry for the
   "subaddress" Sieve extension to point at this document.

5.

6.  Security Considerations

   Security considerations are discussed in [I-D.ietf-sieve-3028bis].
   It is believed that this extension does not introduce any additional
   security concerns.

6.

7.  Normative References

   [I-D.ietf-sieve-3028bis]
              Showalter, T. and P. Guenther, "Sieve: An Email Filtering
              Language", draft-ietf-sieve-3028bis-05 draft-ietf-sieve-3028bis-06 (work in progress),
              November 2005.
              March 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822,
              April 2001.

Appendix A.  Acknowledgments

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

Appendix B.  Changes since RFC3598

   o  Allow detail information to be either or prefix or suffix to  Discussion of how the
      user.

   o  Allow boundary between user and detail parts to be multiple
      characters. information is encoded now
      uses generic language.

   o  Added note regarding processing of local-part with multiple
      separator character sequences. detailing that this extension is most useful when used
      on the envelope "to" address.

   o  Added note detailing that this extension isn't very useful on
      foreign addresses (envelope "from" or originator header fields).

   o  Fixed envelope test example to only use "to" address.

   o  Refer to the zero-length string ("") as "empty" instead of "null"
      (per draft-ietf-sieve-3028bis)

   o  Use only RFC 2606 domains in examples.

   o  Miscellaneous editorial changes.

Author's Address

   Kenneth Murchison
   Carnegie Mellon University
   5000 Forbes Avenue
   Cyert Hall 285
   Pittsburgh, PA  15213
   US

   Phone: +1 412 268 2638
   Email: murch@andrew.cmu.edu

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