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Network Working Group                                       W. SegmullerRequest for Comment: 3431                IBM T.J. Watson Research CenterCategory: Standards Track                                  December 2002Sieve Extension: Relational TestsStatus 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.Copyright Notice   Copyright (C) The Internet Society (2002).  All Rights Reserved.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.1 Introduction   Sieve [SIEVE] is a language for filtering e-mail messages at the time   of final delivery.  It is designed to be implementable on either a   mail client or mail server.  It is meant to be extensible, simple,   and independent of access protocol, mail architecture, and operating   system.  It is suitable for running on a mail server where users may   not be allowed to execute arbitrary programs, such as on black box   Internet Messages Access Protocol (IMAP) servers, as it has no   variables, loops, nor the ability to shell out to external programs.   The RELATIONAL extension 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.Segmuller                   Standards Track                     [Page 1]

RFC 3431           Sieve Extension: Relational Tests       December 2002   The sieve script can also determine the number of fields in the   header, or the number of addresses in a recipient field.  For   example:  are there more than 5 addresses in the to and cc fields.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 [KEYWORDS] and "Syntax:" label for the definition of   action and tagged arguments syntax, and the use of [ABNF].   The capability string associated with extension defined in this   document is "relational".3 Comparators   This document does not define any comparators or exempt any   comparators from the require clause.  Any comparator used, other than   "i;octet" and "i;ascii-casemap", MUST be declared a require clause as   defined in [SIEVE].   The "i;ascii-numeric" comparator, as defined in [ACAP], 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.4 Match Type   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" ) DQUOTESegmuller                   Standards Track                     [Page 2]

RFC 3431           Sieve Extension: Relational Tests       December 20024.1  Match Type Value   The VALUE match type does a relational comparison between strings.   The VALUE match type may be used with any comparator which returns   sort information.   Leading and trailing white space MUST be removed from the value of   the message for the comparison.  White space is defined as                             SP / HTAB / CRLF   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 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 recipients in the specified   fields.  Group names are ignored.   The Envelope Test counts the number of recipients 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.  There is no way a sieve script can determine if the message   was actually sent to someone else using this test.  The envelope   "from" will be 0 if the MAIL FROM is blank, or 1 if MAIL FROM is not   blank.   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,   comparing 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".Segmuller                   Standards Track                     [Page 3]

RFC 3431           Sieve Extension: Relational Tests       December 20025 Security Considerations   Security considerations are discussed in [SIEVE].   An implementation MUST ensure that the test for envelope "to" only   reflects the delivery to the current user.  It MUST not be possible   for a user to determine if this message was delivered to someone else   using this test.6 Example   Using the message:      received: ...      received: ...      subject: example      to: foo@example.com.invalid, baz@example.com.invalid      cc: qux@example.com.invalid   The test:        address :count "ge" :comparator "i;ascii-numeric" ["to", "cc"]      ["3"]      would be true and the test         anyof ( address :count "ge" :comparator "i;ascii-numeric"                         ["to"] ["3"],                 address :count "ge" :comparator "i;ascii-numeric"                         ["cc"] ["3"] )      would be 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 return false.  But         header :count "ge" :comparator "i;ascii-numeric"                          ["received", "subject"] ["3"]      would return true.Segmuller                   Standards Track                     [Page 4]

RFC 3431           Sieve Extension: Relational Tests       December 2002   The test:         header :count "ge" :comparator "i;ascii-numeric"                       ["to", "cc"] ["3"]   will always return 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.7 Extended Example   require ["relational", "comparator-i;ascii-numeric"];   if header :value "lt" :comparator "i;ascii-numeric"             ["x-priority"] ["3"]   {      fileinto "Priority";   }   elseif address :count "gt" :comparator "i;ascii-numeric"              ["to"] ["5"]   {      # everything with more than 5 recipients in the "to" field      # is considered SPAM      fileinto "SPAM";   }   elseif 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.invalid"]   {      fileinto "Only me";   }Segmuller                   Standards Track                     [Page 5]

RFC 3431           Sieve Extension: Relational Tests       December 20028 IANA Considerations   The following template specifies the IANA registration of the Sieve   extension specified in this document:   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: RELATIONAL   Capability keyword: relational   Capability arguments: N/A   Standards Track/IESG-approved experimental RFC number: this RFC   Person and email address to contact for further information:    Wolfgang Segmuller    IBM T.J. Watson Research Center    30 Saw Mill River Rd    Hawthorne, NY 10532    Email: whs@watson.ibm.com   This information should be added to the list of sieve extensions   given onhttp://www.iana.org/assignments/sieve-extensions.9 References9.1 Normative References   [SIEVE]     Showalter, T., "Sieve: A Mail Filtering Language",RFC3028, January 2001.   [Keywords]  Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [ABNF]      Crocker, D., "Augmented BNF for Syntax Specifications:               ABNF",RFC 2234, November 1997.   [RFC2822]   Resnick, P., "Internet Message Format",RFC 2822, April               2001.9.2 Non-Normative References   [ACAP]      Newman, C. and J. G. Myers, "ACAP -- Application               Configuration Access Protocol",RFC 2244, November 1997.Segmuller                   Standards Track                     [Page 6]

RFC 3431           Sieve Extension: Relational Tests       December 200210 Author's Address   Wolfgang Segmuller   IBM T.J. Watson Research Center   30 Saw Mill River Rd   Hawthorne, NY  10532   EMail: whs@watson.ibm.comSegmuller                   Standards Track                     [Page 7]

RFC 3431           Sieve Extension: Relational Tests       December 200211 Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS 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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Segmuller                   Standards Track                     [Page 8]