Archiving of mails

Hi, I’m administering about 20 users running off imap for work and Dreamhost is working perfectly.
I was wondering though, if they create subfolders in Inbox (you can’t anywhere else), and move emails into those, will they also be move to old-messages after the specified number of days?
If so, how do I stop this? I’d be quite happy to not have these moved at all, or to archive the entire directory after a given time.
Cheers & thanks