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Network Working Group                                           C. DabooRequest for Comments: 3685                  Cyrusoft International, Inc.Category: Standards Track                                  February 2004SIEVE Email Filtering: Spamtest and VirusTest ExtensionsStatus 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 (2004).  All Rights Reserved.Abstract   The SIEVE mail filtering language "spamtest" and "virustest"   extensions permit users to use simple, portable commands for spam and   virus tests on email messages.  Each extension provides a new test   using matches against numeric 'scores'.  It is the responsibility of   the underlying SIEVE implementation to do the actual checks that   result in values returned by the tests.Table of Contents1.  Introduction and Overview  . . . . . . . . . . . . . . . . . .22.  SIEVE Extensions . . . . . . . . . . . . . . . . . . . . . . .32.1.  General Considerations . . . . . . . . . . . . . . . . .32.2.  Test spamtest. . . . . . . . . . . . . . . . . . . . . .32.3.  Test virustest . . . . . . . . . . . . . . . . . . . . .43.  Security Considerations  . . . . . . . . . . . . . . . . . . .54.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .64.1.  spamtest registration. . . . . . . . . . . . . . . . . .64.2.  virustest registration . . . . . . . . . . . . . . . . .65.  References . . . . . . . . . . . . . . . . . . . . . . . . . .75.1.  Normative References . . . . . . . . . . . . . . . . . .75.2.  Informative References . . . . . . . . . . . . . . . . .76.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .77.  Intellectual Property Rights Statement . . . . . . . . . . . .78.  Author's Address . . . . . . . . . . . . . . . . . . . . . . .89.  Full Copyright Statement . . . . . . . . . . . . . . . . . . .9Daboo                       Standards Track                     [Page 1]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 20041.  Introduction and Overview   SIEVE scripts are frequently being used to do spam and virus   filtering based on either implicit script tests (e.g., tests for   'black-listed' senders directly encoded in the SIEVE script), or via   testing messages modified by some external spam or virus checker that   handled the message prior to SIEVE.  The use of third-party spam and   virus checker tools poses a problem since each tool has its own way   of indicating the result of its checks.  These usually take the form   of a header added to the message, the content of which indicates the   status using some syntax defined by the particular tool.  Each user   has to then create their own SIEVE scripts to match the contents of   these headers to do filtering.  This requires the script to stay in   synchronization with the third party tool as it gets updated or   perhaps replaced with another.  Thus scripts become tied to specific   environments, and lose portability.   The purpose of this document is to introduce two SIEVE tests that can   be used to implement 'generic' tests for spam and viruses in messages   processed via SIEVE scripts.  These tests return a string containing   a range of numeric values that indicate the severity of spam or   viruses in a message, or a string that indicates the message has not   passed through any spam or virus checking tools.  The spam and virus   checks themselves are handled by the underlying SIEVE implementation   in whatever manner is appropriate, and the implementation maps the   results of these checks into the numeric ranges defined by the new   tests.  Thus a SIEVE implementation can have a spam test that   implicitly checks for third-party spam tool headers and determines   how those map into the spamtest numeric range.   In order to do numeric comparisons against the returned strings,   server implementations MUST also support the SIEVE relational   [RELATIONAL] extension, in addition to the extensions described here.   All examples below assume the relational extension is present.   Conventions for notations are as in [SIEVE]section 1.1, including   use of [KEYWORDS].   The term 'spam' is used in this document to refer to unsolicited or   unwanted email messages.  This document does not attempt to define   what exactly constitutes spam, or how it should be identified, or   what actions should be taken when detected.   The term 'virus' is used in this document to refer to any type of   message whose content can cause malicious damage.  This document does   not attempt to define what exactly constitutes a virus, or how it   should be identified, or what actions should be taken when detected.Daboo                       Standards Track                     [Page 2]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 20042.  SIEVE Extensions2.1.  General Considerations   The "spamtest" and "virustest" tests described below both return a   string that starts with a numeric value, followed by an optional   space (%x20) character and optional arbitrary text.  The numeric   value can be compared to specific values using the SIEVE relational   [RELATIONAL] extension in conjunction with the "i;ascii-numeric"   comparator [ACAP], which will test for the presence of a numeric   value at the start of the string, ignoring any additional text in the   string.  The additional text can be used to carry implementation   specific details about the tests performed and descriptive comments   about the result.  Tests can be done using standard string   comparators against this text if it helps to refine behavior, however   this will break portability of the script as the text will likely be   specific to a particular implementation.2.2.  Test spamtest      Syntax: spamtest [COMPARATOR] [MATCH-TYPE] <value: string>   SIEVE implementations that implement the "spamtest" test have an   identifier of "spamtest" for use with the capability mechanism.   The "spamtest" test evaluates to true if the spamtest result matches   the value.  The type of match is specified by the optional match   argument, which defaults to ":is" if not specified.   The spamtest result is a string starting with a numeric value in the   range "0" (zero) through "10", with meanings summarized below:      spamtest    interpretation      value         0          message was not tested for spam         1          message was tested and is clear of spam         2 - 9      message was tested and has a varying likelihood of                    containing spam in increasing order         10         message was tested and definitely contains spam   The underlying SIEVE implementation will map whatever spam check is   done into this numeric range, as appropriate.Daboo                       Standards Track                     [Page 3]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 2004      Examples:         require ["spamtest", "fileinto",                  "relational", "comparator-i;ascii-numeric"];         if spamtest :value "eq" :comparator "i;ascii-numeric" "0"         {             fileinto "INBOX.unclassified";         }         elsif spamtest :value "ge" :comparator "i;ascii-numeric" "3"         {             fileinto "INBOX.spam-trap";         }   In this example, any message that has not passed through a spam check   tool will be filed into the mailbox "INBOX.unclassified".  Any   message with a spamtest value greater than or equal to "3" is filed   into a mailbox called "INBOX.spam-trap" in the user's mailstore.2.3.  Test virustest      Syntax: virustest [COMPARATOR] [MATCH-TYPE] <value: string>   SIEVE implementations that implement the "virustest" test have an   identifier of "virustest" for use with the capability mechanism.   The "virustest" test evaluates to true if the virustest result   matches the value.  The type of match is specified by the optional   match argument, which defaults to ":is" if not specified.   The virustest result is a string starting with a numeric value in the   range "0" (zero) through "5", with meanings summarized below:      virustest   interpretation      value         0          message was not tested for viruses         1          message was tested and contains no known viruses         2          message was tested and contained a known virus which                    was replaced with harmless content         3          message was tested and contained a known virus                    which was "cured" such that it is now harmless         4          message was tested and possibly contains a                    known virus         5          message was tested and definitely contains a                    known virusDaboo                       Standards Track                     [Page 4]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 2004   The underlying SIEVE implementation will map whatever virus checks   are done into this numeric range, as appropriate.  If the message has   not been categorized by any virus checking tools, then the virustest   result is "0".   Example:      require ["virustest", "fileinto",               "relational", "comparator-i;ascii-numeric"];      if virustest :value "eq" :comparator "i;ascii-numeric" "0"      {          fileinto "INBOX.unclassified";      }      if virustest :value "eq" :comparator "i;ascii-numeric" "4"      {          fileinto "INBOX.quarantine";      }      elsif virustest :value "eq" :comparator "i;ascii-numeric" "5"      {          discard;      }   In this example, any message that has not passed through a virus   check tool will be filed into the mailbox "INBOX.unclassified".  Any   message with a virustest value equal to "4" is filed into a mailbox   called "INBOX.quarantine" in the user's mailstore.  Any message with   a virustest value equal to "5" is discarded (removed) and not   delivered to the user's mailstore.3.  Security Considerations   SIEVE implementations SHOULD ensure that "spamtest" and "virustest"   tests can only occur for messages that have gone through a legitimate   spam or virus check process.  If such checks rely on the addition of   special headers to messages, it is the responsibility of the   implementation to ensure that such headers cannot be spoofed by the   sender, to prevent the implementation from being tricked into   returning the wrong result for the test.   Server administrators MUST ensure that the virus checking tools are   kept up to date, to provide reasonable protection for users using the   "virustest" test.  Users should be made aware of the fact that the   "virustest" test does not provide a 100% reliable way to remove all   viruses, and they should continue to exercise caution when dealing   with messages of unknown content and origin.Daboo                       Standards Track                     [Page 5]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 2004   Beyond that, the "spamtest" and "virustest" extensions do not raise   any security considerations that are not present in the base [SIEVE]   protocol, and these issues are discussed in [SIEVE].4.  IANA Considerations   The following templates specify the IANA registration of the Sieve   extensions specified in this document:4.1.  spamtest registration   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: spamtest   Capability keyword: spamtest   Capability arguments: N/A   Standards Track/IESG-approved RFC XXXX: this RFC   Person and email address to contact for further information:      Cyrus Daboo      Cyrusoft International, Inc.      5001 Baum Blvd., Suite 780,      Pittsburgh, PA 15213      U.S.A.      <mailto:daboo@cyrusoft.com>   This information has been added to the list of sieve extensions given   onhttp://www.iana.org/assignments/sieve-extensions.4.2.  virustest registration   To: iana@iana.org   Subject: Registration of new Sieve extension   Capability name: virustest   Capability keyword: virustest   Capability arguments: N/A   Standards Track/IESG-approved RFC XXXX: this RFC   Person and email address to contact for further information:      Cyrus Daboo      Cyrusoft International, Inc.      5001 Baum Blvd., Suite 780,      Pittsburgh, PA 15213      U.S.A.Daboo                       Standards Track                     [Page 6]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 2004      <mailto:daboo@cyrusoft.com>   This information has been added to the list of sieve extensions given   onhttp://www.iana.org/assignments/sieve-extensions.5.  References5.1.  Normative References   [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [RELATIONAL] Segmuller, W., "Sieve Extension: Relational Tests",RFC3431, December 2002.   [SIEVE]      Showalter, T., "Sieve: A Mail Filtering Language",RFC3028, January 2001.5.2.  Informative References   [ACAP]       Newman, C. and J. Myers, "ACAP -- Application                Configuration Access Protocol",RFC 2244, November 1997.6.  Acknowledgments   Thanks to Tony Hansen, Jutta Degener, Ned Freed, Ashish Gawarikar and   Nigel Swinson for comments and corrections.7.  Intellectual Property Rights Statement   The IETF takes no position regarding the validity or scope of any   intellectual property 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; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication 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 implementors or users of this specification can   be obtained from the IETF Secretariat.Daboo                       Standards Track                     [Page 7]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 2004   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.8.  Author's Address   Cyrus Daboo   Cyrusoft International, Inc.   5001 Baum Blvd., Suite 780,   Pittsburgh, PA 15213   U.S.A.   EMail: daboo@cyrusoft.comDaboo                       Standards Track                     [Page 8]

RFC 3685        SIEVE Spamtest and VirusTest Extensions    February 20049.  Full Copyright Statement   Copyright (C) The Internet Society (2004).  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 assignees.   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.Daboo                       Standards Track                     [Page 9]