[SOLVED] scheduled empty trash emtpy junk for users

[ArcaneMagus]

This is beyond me then, since it looks like it is scanning the mailboxes and deleting messages, just not all that it should.

In the admin UI look at Class of Service -> (whichever one applies to your account) -> Advanced -> Email Retention Policy for the number of days messages should be kept.
You can also check with:

zmprov gc default | grep -i lifetime