Determines the time between Deferred queue scans by the queue manager.

This time should be less than or equal to the minimal_backoff_time setting.

Determines the minimum time between attempts to deliver a deferred message. When a message is first placed in the Deferred queue, the value of this setting is what determines when the first attempt to redeliver the message is made.

This time should be equal to or greater than the queue_run_delay setting.

Determines the maximum time between attempts to deliver a message. The time between each attempt to deliver a deferred message will grow exponentially until it reaches the value in this setting.

The attempted deliveries are repeated at this value until the maximal_queue_lifetime is reached.

Determines the message life time in the Deferred queue. Once the this lifetime expires, messages in the Deferred queue are returned to the sender with an "undelivered" notice.