A radically different approach would be to introduce a new 'expired'
queue and move messages there when they need to be expired, and to
introduce a new postqueue flag to flush the expired queue (the queue
manager should not normally scan the expired queue because that
would slow down all deliveries).
Pro: Less complexity. No 'expired' state inside queue files.
Con: More complexity. When expired mail needs to be deferred because
the bounce daemon is failing, it should go back to the expired
queue, not to the deferred queue.
Wietse
