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rfc:rfc5233

Network Working Group K. Murchison Request for Comments: 5233 Carnegie Mellon University Obsoletes: 3598 January 2008 Category: Standards Track

            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.

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 Email Filtering
 Language that allows users to compare against the user and detail
 sub-parts of an address.

Table of Contents

 1. Introduction ....................................................2
 2. Conventions Used in This Document ...............................2
 3. Capability Identifier ...........................................2
 4. Subaddress Comparisons ..........................................2
 5. IANA Considerations .............................................5
 6. Security Considerations .........................................5
 7. Normative References ............................................5
 Appendix A. Acknowledgments ........................................6
 Appendix B. Changes since RFC 3598 .................................6

Murchison Standards Track [Page 1] RFC 5233 Sieve: Subaddress Extension January 2008

1. Introduction

 Subaddressing is the practice of augmenting the local-part of an
 [RFC2822] address with some 'detail' information in order to give
 some extra meaning to that address.  One common way of encoding
 'detail' information into the local-part is to add a 'separator
 character 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.com" is delivered to
    the voice mailbox number "123" at phone number "5551212".
 This document describes an extension to the Sieve language defined by
 [RFC5228] for comparing against the 'user' and 'detail' sub-parts of
 an address.

2. Conventions Used in This Document

 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].

3. Capability Identifier

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

4. Subaddress Comparisons

 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,

Murchison Standards Track [Page 2] RFC 5233 Sieve: Subaddress Extension January 2008

    aliases, and 'virtual domains' are involved since the envelope may
    be the only source of detail information for the specific
    recipient.
    NOTE: Because the encoding of detailed addresses 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.  If the address is 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.  If the address is not encoded to contain a
 detail sub-part, then the address fails to match any of the specified
 keys.  If a zero-length string is encoded as the detail sub-part,
 then ":detail" resolves to the empty value ("").
    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 encoding method used for
 detailed addresses matches that which is used and/or allowed by the
 encompassing mail system, otherwise unexpected results might occur.
 Note that the mechanisms used to define and/or query the 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 [RFC5228],
 Section 2.7.4.
 For convenience, the "ADDRESS-PART" syntax element defined in
 [RFC5228], Section 2.7.4, is augmented here as follows:
       ADDRESS-PART  =/  ":user" / ":detail"
 A diagram showing the ADDRESS-PARTs of an email address where the
 detail information follows a separator character sequence of "+" is
 shown below:

Murchison Standards Track [Page 3] RFC 5233 Sieve: Subaddress Extension January 2008

        :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 ["envelope", "subaddress", "fileinto"];
    # In this example the same user account receives mail for both
    # "ken@example.com" and "postmaster@example.com"
    # File all messages to postmaster into a single mailbox,
    # ignoring the :detail part.
    if envelope :user "to" "postmaster" {
        fileinto "inbox.postmaster";
        stop;
    }
    # File mailing list messages (subscribed as "ken+mta-filters").
    if envelope :detail "to" "mta-filters" {
        fileinto "inbox.ietf-mta-filters";
    }
    # Redirect all mail sent to "ken+foo".
    if envelope :detail "to" "foo" {
        redirect "ken@example.net";
    }

Murchison Standards Track [Page 4] RFC 5233 Sieve: Subaddress Extension January 2008

5. IANA Considerations

 The following template specifies the IANA registration of the
 subaddress Sieve extension specified in this document.  This
 registration replaces that from RFC 3598:
 To: iana@iana.org
 Subject: Registration of new Sieve extension
 Capability name: subaddress
 Description:     Adds the ':user' and ':detail' address parts
                  for use with the address and envelope tests
 RFC number:      RFC 5233
 Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>
 This information has been added to the list of Sieve extensions given
 on http://www.iana.org/assignments/sieve-extensions.

6. Security Considerations

 Security considerations are discussed in [RFC5228].  It is believed
 that this extension does not introduce any additional security
 concerns.

7. Normative References

 [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.
 [RFC5228]  Guenther, P., Ed., and T. Showalter, Ed., "Sieve: An Email
            Filtering Language", RFC 5228, January 2008.

Murchison Standards Track [Page 5] RFC 5233 Sieve: Subaddress Extension January 2008

Appendix A. Acknowledgments

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

Appendix B. Changes since RFC 3598

 o  Discussion of how the user and detail information is encoded now
    uses generic language.
 o  Added note 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  Replaced ":user" example with one that doesn't produce unexpected
    behavior.
 o  Refer to the zero-length string ("") as "empty" instead of "null"
    (per RFC 5228).
 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
 USA
 Phone: +1 412 268 2638
 EMail: murch@andrew.cmu.edu

Murchison Standards Track [Page 6] RFC 5233 Sieve: Subaddress Extension January 2008

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 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Murchison Standards Track [Page 7]

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