Message tracking and recall

A general message tracking and recall facility has been implemented. The tracking aspect of this facility conforms to RFC 3885, RFC 3886, and RFC 3887. The recall aspect is implemented as a tracking extension. Additionally, some tracking extensions have been implemented to make it possible for a tracking client to track and recall messages submitted by a non-tracking client.

In order to enable message tracking and recall, a memcache server must be operating, and the  MTA option must be set to   to enable use of memcache for message tracking purposes. Which messages get tracking information stored is controlled by various message tracking channel options.

See also:
 * Message tracking and recall setup and configuration
 * Message tracking channel options
 * Message tracking MTA options