If it isn't doing scan to mailbox (hdd is filling over time because they don't delete the jobs when done) then there are only 2 options
The Fix and the stop gap.
Fix = Altboot no data backup no clone to latest firmware
This is not a Connectkey known issue on any firmware, so the issue is this machine specific, corruption or a hardware failure. Corruption can't survive this process, but of course you will have to set up everything all over again from scratch.
Stop gap = Set the mailboxes to delete files older than x amount of days, and set Secure disk image overwrite to happen daily when nobody is there.
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.