Duplicate Extension

Relevant specifications
=======================

	doc/rfc/draft-ietf-appsawg-sieve-duplicate-03.txt

Description
===========

The duplicate extension augments the Sieve filtering implementation with a test
to verify whether the evaluated string value was seen before in an earlier
execution of the Sieve script. The main application for this new test is 
detecting and handling duplicate message deliveries, e.g. as caused by
mailinglists when people reply both to the mailinglist and the user directly.

Refer to doc/rfc/draft-ietf-appsawg-sieve-duplicate-03.txt for a specification
of the Sieve language extension. Previously, this extension was Dovecot-specific
and available under the name "vnd.dovecot.duplicate". That implementation
differs significantly from what is now published as an internet draft, but
for backwards compatibility the original extension is still supported.

Configuration
=============

The "duplicate" extension is not enabled by default. 

The following configuration settings are used:

sieve_duplicate_default_period = 14d
sieve_duplicate_max_period = 7d
  These options respectively specify the default and the maximum value for the
  period after which tracked values are purged from the duplicate tracking
  database. The period is specified in s(econds), unless followed by a d(ay),
  h(our) or m(inute) specifier character.

Example
=======

plugin {
  sieve = ~/.dovecot.sieve

  sieve_extensions = +vnd.dovecot.duplicate

  sieve_duplicate_default_period = 1h
	sieve_duplicate_max_period = 1d
}d