Sieve Email Filtering: Spamtest and Virustest Extensions
RFC 5235

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Network Working Group                                           C. Daboo
Request for Comments: 5235                                  January 2008
Obsoletes: 3685
Category: Standards Track

        Sieve Email Filtering: Spamtest and Virustest Extensions

Status 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

   The Sieve email filtering language "spamtest", "spamtestplus", 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 proper input to the tests.

Table of Contents

   1. Introduction and Overview .......................................2
   2. Conventions Used in This Document ...............................2
   3. Sieve Extensions ................................................3
      3.1. General Considerations .....................................3
      3.2. Test spamtest ..............................................3
           3.2.1. spamtest without :percent Argument ..................4
           3.2.2. spamtest with :percent Argument .....................5
      3.3. Test virustest .............................................7
   4. Security Considerations .........................................9
   5. IANA Considerations .............................................9
      5.1. spamtest Registration ......................................9
      5.2. virustest Registration ....................................10
      5.3. spamtestplus Registration .................................10
   6. References .....................................................10
      6.1. Normative References ......................................10
      6.2. Informative References ....................................11
   Appendix A. Acknowledgments .......................................12
   Appendix B. Important Changes since RFC 3685 ......................12

Daboo                       Standards Track                     [Page 1]
RFC 5235        Sieve: Spamtest and Virustest Extensions    January 2008

1.  Introduction and Overview

   Sieve scripts are frequently being used to do spam and virus
   filtering either based on 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.  The spam and virus checks themselves
   are handled by the underlying Sieve implementation in whatever manner
   is appropriate, so that the Sieve spam and virus test commands can be
   used in a portable way.

   In order to do numeric comparisons against the returned strings,
   server implementations MUST also support the Sieve relational
   [RFC5231] extension, in addition to the extensions described here.
   All examples below assume the relational extension is present.

2.  Conventions Used in This Document

   Conventions for notations are as in [RFC5228] Section 1.1.

   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].

   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.