Sieve Email Filtering: Detecting Duplicate Deliveries
RFC 7352

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Internet Engineering Task Force (IETF)                          S. Bosch
Request for Comments: 7352                                September 2014
Category: Standards Track
ISSN: 2070-1721

         Sieve Email Filtering: Detecting Duplicate Deliveries

Abstract

   This document defines a new test command, "duplicate", for the Sieve
   email filtering language.  This test adds the ability to detect
   duplications.  The main application for this new test is handling
   duplicate deliveries commonly caused by mailing list subscriptions or
   redirected mail addresses.  The detection is normally performed by
   matching the message ID to an internal list of message IDs from
   previously delivered messages.  For more complex applications, the
   "duplicate" test can also use the content of a specific header field
   or other parts of the message.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7352.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Bosch                        Standards Track                    [Page 1]
RFC 7352          Sieve: Detecting Duplicate Deliveries   September 2014

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................3
   3. Test "duplicate" ................................................3
      3.1. Arguments ":header" and ":uniqueid" ........................5
      3.2. Argument ":handle" .........................................7
      3.3. Arguments ":seconds" and ":last" ...........................8
      3.4. Interaction with Other Sieve Extensions ....................9
   4. Sieve Capability Strings ........................................9
   5. Examples ........................................................9
      5.1. Example 1 ..................................................9
      5.2. Example 2 .................................................10
      5.3. Example 3 .................................................11
      5.4. Example 4 .................................................12
   6. Security Considerations ........................................12
   7. IANA Considerations ............................................13
   8. Acknowledgements ...............................................14
   9. References .....................................................14
      9.1. Normative References ......................................14
      9.2. Informative References ....................................15

1.  Introduction

   This document specifies an extension to the Sieve filtering language
   defined by RFC 5228 [SIEVE].  It adds a test to track whether or not
   a text string was seen before by the delivery agent in an earlier
   execution of the Sieve script.  This can be used to detect and handle
   duplicate message deliveries.

   Duplicate deliveries are a common side effect of being subscribed to
   a mailing list.  For example, if a member of the list decides to
   reply to both the user and the mailing list itself, the user will
   often get one copy of the message directly and another through the
   mailing list.  Also, if someone crossposts over several mailing lists
   to which the user is subscribed, the user will likely receive a copy
   from each of those lists.  In another scenario, the user has several
   redirected mail addresses all pointing to his main mail account.  If
   one of the user's contacts sends the message to more than one of
   those addresses, the user will likely receive more than a single
   copy.  Using the "duplicate" extension, users have the means to
   detect and handle such duplicates (e.g., by discarding them, marking
   them as "seen", or putting them in a special folder).

Bosch                        Standards Track                    [Page 2]