Sieve filter duplicate extension MTA options

As of 8.0, the MTA supports the Sieve duplicate extension specified in RFC 7352.

Several MTA options relate to this support. In particular, the  MTA option specifies where duplicate tracking information should be stored. At present, the value must be a   URL of the form: memcache://host:port/key-prefix If the host isn&#x27;t specified, it defaults to the value of the  MTA option. It is an error for  not to be set in this case. If the port isn&#x27;t specified, it defaults to the value of the   MTA option; if that option in turn isn&#x27;t specified, the default is 11211, the usual port for memcache servers. , if specified, is prepended to the keys the duplicate extension sends to the memcache server.

Note that duplicate tests are performed during Sieve evaluation but no memcache updates are performed. It is only after the message has been successfully processed that updates are done.

Also note that duplicate information is implicitly qualified by the owner of the Sieve. In the case of system-level Sieves, this will be the applicable postmaster address, so system-level Sieves operate in shared namespace(s). Note that the  argument can be used to force system-level Sieves to operate in their own namespace.

See also:
 * duplicate_minimum_timeout MTA Option
 * duplicate_maximum_timeout MTA Option
 * duplicate_timeout_default MTA Option
 * duplicate_tracking_url MTA Option
 * max_duplicates MTA Option
 * memcache_host Option
 * memcache_port Option
 * MTA URL types
 * Sieve duplicate extension
 * Sieve hierarchy
 * Sieve filter MTA options