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Network Working Group                                       K. MurchisonRequest for Comments: 5233                    Carnegie Mellon UniversityObsoletes:3598                                             January 2008Category: Standards TrackSieve Email Filtering: Subaddress ExtensionStatus 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 Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................23. Capability Identifier ...........................................24. Subaddress Comparisons ..........................................25. IANA Considerations .............................................56. Security Considerations .........................................57. Normative References ............................................5Appendix A. Acknowledgments ........................................6Appendix B. Changes sinceRFC 3598 .................................6Murchison                   Standards Track                     [Page 1]

RFC 5233              Sieve: Subaddress Extension           January 20081.  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 20085.  IANA Considerations   The following template specifies the IANA registration of the   subaddress Sieve extension specified in this document.  This   registration replaces that fromRFC 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   onhttp://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 2008Appendix 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 sinceRFC 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"      (perRFC 5228).   o  Use onlyRFC 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.eduMurchison                   Standards Track                     [Page 6]

RFC 5233              Sieve: Subaddress Extension           January 2008Full Copyright Statement   Copyright (C) The IETF Trust (2008).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   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   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights 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; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Murchison                   Standards Track                     [Page 7]