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Versions: (RFC 3431) 00 01 02 03 04 RFC 5231

Sieve Working Group                                         W. Segmuller
Internet Draft                                                  B. Leiba
Obsoletes: 3431 (if approved)            IBM T.J. Watson Research Center
Document: draft-ietf-sieve-3431bis-00.txt                  February 2005
                                                     Expires August 2005

                   Sieve Extension: Relational Tests

Status of this Document
   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.
   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at
   This Internet-Draft will expire on August 14, 2005.
Copyright Notice
   Copyright (C) The Internet Society (2005).
   This document describes the RELATIONAL extension to the Sieve mail
   filtering language defined in RFC 3028.  This extension extends
   existing conditional tests in Sieve to allow relational operators.
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   In addition to testing their content, it also allows for testing of
   the number of entities in header and envelope fields.
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
   "relational" extension to the Sieve mail filtering language,
   available from the RFC repository as
   This document and the Sieve language itself are being discussed on
   the MTA Filters mailing list at <mailto:ietf-mta-filters@imc.org>.
   Subscription requests can be sent to
   <mailto:ietf-mta-filters-request@imc.org?body=subscribe> (send an
   email message with the word "subscribe" in the body).  More
   information on the mailing list along with a WWW archive of back
   messages is available at <http://www.imc.org/ietf-mta-filters/>.
Conventions used in this document
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 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".
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
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   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: are there more than 5 addresses in the to and cc fields.
2. 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.
3. Match Type
   This document defines two new match types.  They are the VALUE match
   type and the COUNT match type.
   The syntax is:
       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 "<=".
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          ; "eq" means "greater than", the C operator "==".
          ; "ne" means "greater than", the C operator "!=".
3.1.  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.
3.2.  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
   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
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   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".
4. 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.
   The test:
       header :count "ge" :comparator "i;ascii-numeric"
                       ["to", "cc"] ["3"]
   will always return false on an RFC 2822 compliant message [RFC2822],
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   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
5. 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";
6.  IANA Considerations
   This document requests that the IANA update the entry for the
   "relational" Sieve extension to point to this document.
7. Security Considerations
   Security considerations are discussed in [SIEVE].
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   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.
8. Normative References
   [SIEVE]; Showalter, T.; "Sieve: A Mail Filtering Language"; RFC 3028;
   January 2001.
   [Keywords]; Bradner, S.; "Key words for use in RFCs to
   IndicateRequirement 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
9. Non-Normative References
   [ACAP]; Newman, C. and J. G. Myers; "ACAP -- Application
   Configuration Access Protocol"; RFC 2244; November 1997.
10. Authors' Addresses
   Wolfgang Segmuller
   IBM T.J. Watson Research Center
   19 Skyline Drive
   Hawthorne, NY  10532
   Phone: 1-914-784-7408
   Email: whs@watson.ibm.com
   Barry Leiba
   IBM T.J. Watson Research Center
   19 Skyline Drive
   Hawthorne, NY  10532
   Phone: 1-914-784-7941
   Email: leiba@watson.ibm.com
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