Maildir filling up with files

My maildir/new folder is filling up with files (almost 1700 files and 600MB so far) yet none of my users have anything near even 1MB of mail. With just a half dozen email users, this is quite a lot of storage being used. These files have been accumulating since march of '05 when I created my account. I would like to get rid of most of these. Is it safe to delete all but the most recent files and still keep the new messages?

Do you have Spam filtering on, and do you ever delete the junk messages? I’d check that first. I’d be leary of deleting messages without knowing what they were, and being sure it wasn’t somthing I wanted.