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+Pigeonhole Sieve: Duplicate Extension
+=====================================
+
+The *duplicate* extension RFC 7353 [http://tools.ietf.org/html/rfc7352] 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.
+
+Previously, this extension was Dovecot-specific and available under the name
+'vnd.dovecot.duplicate'. Specification for old version available here
+[http://hg.rename-it.nl/dovecot-2.1-pigeonhole/raw-file/tip/doc/rfc/spec-bosch-sieve-duplicate.txt].
+That implementation differs significantly from what is now published as RFC
+7353 [http://tools.ietf.org/html/rfc7352], but the original extension is still
+supported for backwards compatibility.
+
+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
+}
+---%<-------------------------------------------------------------------------
+
+(This file was created from the wiki on 2019-06-19 12:42)