There is no guarantee that mail goes from incoming->qmgr only once. Whenever the qmgr is restarted, mail goes back from active queue to incoming queue, so that it doesn't drown in a sea of deferred mail.
If your problem is a large incoming queue, then I suggest that you
take the necessary step to find out why Postfix defers massive
amounts of mail in the first place; everything else, including
upgrading Postfix, is just a workaround for a problem that need
not exist.
Wietse
