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queue_run_delay (default: 300 seconds; before Postfix 2.4: 1000s)
How often the queue manager scans the queue for deferred mail.
minimal_backoff_time (default: 300 seconds; before Postfix 2.4: 1000s)
The minimal amount of time a message won't be looked at, and the minimal amount of time to stay away from a "dead" destination.
maximal_backoff_time (default: 4000 seconds)
The maximal amount of time a message won't be looked at after a delivery failure.
maximal_queue_lifetime (default: 5 days)
How long a message stays in the queue before it is sent back as undeliverable. Specify 0 for mail that should be returned immediately after the first unsuccessful delivery attempt.
bounce_queue_lifetime (default: 5 days, available with Postfix version 2.1 and later)
How long a MAILER-DAEMON message stays in the queue before it is considered undeliverable. Specify 0 for mail that should be tried only once.
qmgr_message_recipient_limit (default: 20000)
The size of many in-memory queue manager data structures. Among others, this parameter limits the size of the short-term, in-memory list of "dead" destinations. Destinations that don't fit the list are not added.
transport_destination_concurrency_failed_cohort_limit
Controls when a destination is considered "dead". This parameter is critical with a non-zero transport_destination_rate_delay, with a reduced transport_destination_concurrency_limit, or with a reduced initial_destination_concurrency.