Sieve Working Group                                         K. Murchison
Internet-Draft                                        Oceana Matrix Ltd.                                Carnegie Mellon University
Obsoletes: 3598 (if approved)                         September 12, 2005                          February 15, 2006
Expires: March 16, August 19, 2006

             Sieve Email Filtering -- Subaddress Extension

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Copyright Notice

   Copyright (C) The Internet Society (2005). (2006).


   On email systems that allow for "subaddressing" or "detailed
   addressing" (e.g., ""), 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.

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
   <> and

   This document and the Sieve language itself are being discussed on
   the MTA Filters mailing list at <>.
   Subscription requests can be sent to
   <> (send an
   email message with the word "subscribe" in the body).  More
   information on the mailing list along with a WWW an archive of back
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Capability Identifier  . . . . . . . . . . . . . . . . . . . .  5
   3.  Subaddress Comparisons . . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  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 (either by prefix or (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 "separator character
   sequence" (typically "+"), forms the 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

   Typical uses of subaddressing might be:

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

   o  A message addressed to "" 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.

   Conventions for notations are as in [I-D.ietf-sieve-3028bis] section
   1.1, including use of [RFC2119].

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

      NOTE: Because the construction of detailed addresses can be 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

   The ":user" argument specifies the user sub-part of the local-part of
   an address.  Whether  The positioning of the user sub-part lies with respect to the left or right of
   separator character sequence is dependent on the encompassing mail
   system.  If no separator character sequence exists, then ":user"
   specifies the entire left-side of the address (equivalent to

   The ":detail" argument specifies the detail sub-part of the local-
   part of an address.  Whether  The positioning of the detail sub-part lies with
   respect to the left or
   right of the separator character sequence is dependent on the
   encompassing mail system.  If no separator character sequence exists,
   the test evaluates to false.  If the separator character sequence
   exists, but not no detail information is provided, then ":detail" ":is"
   the empty key ("").  Otherwise, the ":detail" sub-part ":contains"
   the empty key.

      NOTE: If the separator character sequence occurs more than once in
      the local-part, then the address MUST be logic used to split at the left-most
      separator when the detail information address is a suffix
      implementation defined, and at is usually dependent on the
      right-most separator when format
      used by the detail information is a prefix. encompassing mail system.

   Implementations MUST make sure that the separator character sequence
   and the ordering of the user and detail sub-parts match those that
   are 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 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-

   For convenience, the "ADDRESS-PART" syntax element defined in
   [I-D.ietf-sieve-3028bis] 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

   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
   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"] "") {

      # Redirect all mail sent to +foo.
      if envelope :detail "to" "foo" {
        redirect "";

4.  IANA Considerations

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

5.  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.  Normative References

              Showalter, T. and P. Guenther, "Sieve: An Email Filtering
              Language", draft-ietf-sieve-3028bis-04 draft-ietf-sieve-3028bis-05 (work in progress),
              November 2005.

   [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 Jutta Degener for their help with this

Appendix B.  Changes since RFC3598

   o  Allow detail information to be either or prefix or suffix to the

   o  Allow boundary between user and detail parts to be multiple

   o  Added note regarding processing of local-part with multiple
      separator character sequences.

   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  Miscellaneous editorial changes.

Author's Address

   Kenneth Murchison
   Oceana Matrix Ltd.
   2495 Main St.
   Suite 401
   Buffalo, NY  14214
   Carnegie Mellon University
   5000 Forbes Avenue
   Cyert Hall 285
   Pittsburgh, PA  15213

   Phone: +1 716 604 0088 412 268 2638

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