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Network Working Group                                       W. SegmullerRequest for Comments: 5231                                      B. LeibaObsoletes:3431                          IBM T.J. Watson Research CenterCategory: Standards Track                                   January 2008Sieve Email Filtering: Relational 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   This document describes the RELATIONAL extension to the Sieve mail   filtering language defined inRFC 3028.  This extension extends   existing conditional tests in Sieve to allow relational operators.   In addition to testing their content, it also allows for testing of   the number of entities in header and envelope fields.   This document obsoletesRFC 3431.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions Used in This Document . . . . . . . . . . . . . . .23.  Comparators . . . . . . . . . . . . . . . . . . . . . . . . . .24.  Match Types . . . . . . . . . . . . . . . . . . . . . . . . . .34.1.  Match Type VALUE  . . . . . . . . . . . . . . . . . . . . .34.2.  Match Type COUNT  . . . . . . . . . . . . . . . . . . . . .35.  Interaction with Other Sieve Actions  . . . . . . . . . . . . .46.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . .47.  Extended Example  . . . . . . . . . . . . . . . . . . . . . . .68.  Changes sinceRFC 3431  . . . . . . . . . . . . . . . . . . . .69.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .710. Security Considerations . . . . . . . . . . . . . . . . . . . .711. Normative References  . . . . . . . . . . . . . . . . . . . . .7Segmuller & Leiba           Standards Track                     [Page 1]

RFC 5231              Sieve: Relational Extension           January 20081.  Introduction   The RELATIONAL extension to the Sieve mail filtering language [Sieve]   provides relational operators on the address, envelope, and header   tests.  This extension also provides a way of counting the entities   in a message header or address field.   With this extension, the Sieve script may now determine if a field is   greater than or less than a value instead of just equivalent.  One   use is for the x-priority field: move messages with a priority   greater than 3 to the "work on later" folder.  Mail could also be   sorted by the from address.  Those userids that start with 'a'-'m' go   to one folder, and the rest go to another folder.   The Sieve script can also determine the number of fields in the   header, or the number of addresses in a recipient field, for example,   whether there are more than 5 addresses in the to and cc fields.   The capability string associated with the extension defined in this   document is "relational".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 inBCP 14,RFC 2119.   Conventions for notations are as in [Sieve]section 1.1, including   the use of [Kwds] and the use of [ABNF].3.  Comparators   This document does not define any comparators or exempt any   comparators from the require clause.  Any comparator used must be   treated as defined in [Sieve].   The "i;ascii-numeric" comparator, as defined in [RFC4790], MUST be   supported for any implementation of this extension.  The comparator   "i;ascii-numeric" MUST support at least 32-bit unsigned integers.   Larger integers MAY be supported.  Note: the "i;ascii-numeric"   comparator does not support negative numbers.Segmuller & Leiba           Standards Track                     [Page 2]

RFC 5231              Sieve: Relational Extension           January 20084.  Match Types   This document defines two new match types.  They are the VALUE match   type and the COUNT match type.   The syntax is:   MATCH-TYPE =/ COUNT / VALUE   COUNT = ":count" relational-match   VALUE = ":value" relational-match   relational-match = DQUOTE           ("gt" / "ge" / "lt" / "le" / "eq" / "ne") DQUOTE           ; "gt" means "greater than", the C operator ">".           ; "ge" means "greater than or equal", the C operator ">=".           ; "lt" means "less than", the C operator "<".           ; "le" means "less than or equal", the C operator "<=".           ; "eq" means "equal to", the C operator "==".           ; "ne" means "not equal to", the C operator "!=".4.1.  Match Type VALUE   The VALUE match type does a relational comparison between strings.   The VALUE match type may be used with any comparator that returns   sort information.   A value from the message is considered the left side of the relation.   A value from the test expression, the key-list for address, envelope,   and header tests, is the right side of the relation.   If there are multiple values on either side or both sides, the test   is considered true if any pair is true.4.2.  Match Type COUNT   The COUNT match type first determines the number of the specified   entities in the message and does a relational comparison of the   number of entities, as defined below, to the values specified in the   test expression.   The COUNT match type SHOULD only be used with numeric comparators.   The Address Test counts the number of addresses (the number of   "mailbox" elements, as defined in [RFC2822]) in the specified fields.   Group names are ignored, but the contained mailboxes are counted.Segmuller & Leiba           Standards Track                     [Page 3]

RFC 5231              Sieve: Relational Extension           January 2008   The Envelope Test counts the number of addresses in the specified   envelope parts.  The envelope "to" will always have only one entry,   which is the address of the user for whom the Sieve script is   running.  Using this test, there is no way a Sieve script can   determine if the message was actually sent to someone else.  The   envelope "from" will be 0 if the MAIL FROM is empty, or 1 if MAIL   FROM is not empty.   The Header Test counts the total number of instances of the specified   fields.  This does not count individual addresses in the "to", "cc",   and other recipient fields.   In all cases, if more than one field name is specified, the counts   for all specified fields are added together to obtain the number for   comparison.  Thus, specifying ["to", "cc"] in an address COUNT test   compares the total number of "to" and "cc" addresses; if separate   counts are desired, they must be done in two comparisons, perhaps   joined by "allof" or "anyof".5.  Interaction with Other Sieve Actions   This specification adds two match types.  The VALUE match type only   works with comparators that return sort information.  The COUNT match   type only makes sense with numeric comparators.   There is no interaction with any other Sieve operations, nor with any   known extensions.  In particular, this specification has no effect on   implicit KEEP, nor on any explicit message actions.6.  Example   Using the message:      received: ...      received: ...      subject: example      to: foo@example.com, baz@example.com      cc: qux@example.com   The test:      address :count "ge" :comparator "i;ascii-numeric"                      ["to", "cc"] ["3"]   would evaluate to true, and the testSegmuller & Leiba           Standards Track                     [Page 4]

RFC 5231              Sieve: Relational Extension           January 2008      anyof ( address :count "ge" :comparator "i;ascii-numeric"                      ["to"] ["3"],              address :count "ge" :comparator "i;ascii-numeric"                      ["cc"] ["3"] )   would evaluate to false.   To check the number of received fields in the header, the following   test may be used:      header :count "ge" :comparator "i;ascii-numeric"                      ["received"] ["3"]   This would evaluate to false.  But      header :count "ge" :comparator "i;ascii-numeric"                      ["received", "subject"] ["3"]   would evaluate to true.   The test:      header :count "ge" :comparator "i;ascii-numeric"                      ["to", "cc"] ["3"]   will always evaluate to false on anRFC 2822 compliant message   [RFC2822], since a message can have at most one "to" field and at   most one "cc" field.  This test counts the number of fields, not the   number of addresses.Segmuller & Leiba           Standards Track                     [Page 5]

RFC 5231              Sieve: Relational Extension           January 20087.  Extended Example      require ["relational", "comparator-i;ascii-numeric", "fileinto"];      if header :value "lt" :comparator "i;ascii-numeric"                ["x-priority"] ["3"]      {         fileinto "Priority";      }      elsif address :count "gt" :comparator "i;ascii-numeric"                 ["to"] ["5"]      {         # everything with more than 5 recipients in the "to" field         # is considered SPAM         fileinto "SPAM";      }      elsif address :value "gt" :all :comparator "i;ascii-casemap"                 ["from"] ["M"]      {         fileinto "From N-Z";      } else {         fileinto "From A-M";      }      if allof ( address :count "eq" :comparator "i;ascii-numeric"                         ["to", "cc"] ["1"] ,                 address :all :comparator "i;ascii-casemap"                         ["to", "cc"] ["me@foo.example.com"] )      {         fileinto "Only me";      }8.  Changes sinceRFC 3431   Apart from several minor editorial/wording changes, the following   list describes the notable changes to this specification sinceRFC3431.   o  Updated references, including changing the comparator reference      from the Application Configuration Access Protocol (ACAP) to the      "Internet Application Protocol Collation Registry" document      [RFC4790].   o  Updated and corrected the examples.Segmuller & Leiba           Standards Track                     [Page 6]

RFC 5231              Sieve: Relational Extension           January 2008   o  Added definition comments to ABNF for "gt", "lt", etc.   o  Clarified whatRFC 2822 elements are counted in the COUNT test.   o  Removed the requirement to strip white space from header fields      before comparing; a more general version of this requirement has      been added to the Sieve base spec.9.  IANA Considerations   The following template specifies the IANA registration of the   relational Sieve extension specified in this document:   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: relational   Description:     Extends existing conditional tests in Sieve language                    to allow relational operators   RFC number:RFC 5231   Contact address: The Sieve discussion list <ietf-mta-filters@imc.org>10.  Security Considerations   An implementation MUST ensure that the test for envelope "to" only   reflects the delivery to the current user.  Using this test, it MUST   not be possible for a user to determine if this message was delivered   to someone else.   Additional security considerations are discussed in [Sieve].11.  Normative References   [ABNF]     Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF",RFC 4234, October 2005.   [Kwds]     Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",RFC 2119, March 1997.   [RFC2822]  Resnick, P., "Internet Message Format",RFC 2822,              April 2001.   [RFC4790]  Newman, C., Duerst, M., and A. Gulbrandsen, "Internet              Application Protocol Collation Registry",RFC 4790,              March 2007.   [Sieve]    Guenther, P., Ed. and T. Showalter, Ed., "Sieve: An Email              Filtering Language",RFC 5228, January 2008.Segmuller & Leiba           Standards Track                     [Page 7]

RFC 5231              Sieve: Relational Extension           January 2008Authors' Addresses   Wolfgang Segmuller   IBM T.J. Watson Research Center   19 Skyline Drive   Hawthorne, NY  10532   US   Phone: +1 914 784 7408   EMail: werewolf@us.ibm.com   Barry Leiba   IBM T.J. Watson Research Center   19 Skyline Drive   Hawthorne, NY  10532   US   Phone: +1 914 784 7941   EMail: leiba@watson.ibm.comSegmuller & Leiba           Standards Track                     [Page 8]

RFC 5231              Sieve: Relational 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.Segmuller & Leiba           Standards Track                     [Page 9]