bounce_queue_lifetime (default: 5d)
The maximal time a bounce message is queued before it is considered undeliverable. By default, this is the same as the queue life time for regular mail.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks). The default time unit is d (days).

Specify 0 when mail delivery should be tried only once.

This feature is available in Postfix 2.1 and later.