Duplicate Extension

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

	doc/rfc/duplicate.rfc7352.txt

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

The "duplicate" extension adds a new test command called "duplicate" to the
Sieve 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.

Refer to doc/rfc/duplicate.rfc7352.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 RFC, but for backwards compatibility the original
extension is still supported.

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

The "duplicate" extension is available by default. The "duplicate" extension has
its own specific settings. The following settings are available (default
values are indicated):

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_duplicate_default_period = 1h
	sieve_duplicate_max_period = 1d
}