Name: duplicatesuppression
Type: SWITCH
Default-Value: 1
Last-Modified: 2.3.17

If enabled, lmtpd will suppress delivery of a message to a mailbox if a
message with the same message-id (or resent-message-id) is recorded as
having already been delivered to the mailbox.  Records the mailbox and
message-id/resent-message-id of all successful deliveries.
