Clean Incoming Mail Queue
This setting determines how long "done" mail messages will remain in the Incoming Mail queue. Specifically, the incoming mail queue will display xx days worth of incoming mail messages
which are "done". Keep in mind that this only removes the messages from view, however they are still in the database (for non-SQL versions) and will remain so until the "dbupgrade" utility is run.
Choosing "0" will result in all messages being shown until they are removed from the database.