If you are worried about the 16 gig limit and you have enough disk space for archived email and PSTs. Why don't you start moving the old messages out of the exchange db and into archives and psts. Just be sure you backup the PSTs and split them up by month. For each user have a monthly PST they can reference, may.pst, june.pst ....This could be for their archives, the don't have to be open , just available for the user. Start to slowly move mail from the db, to PSTs, to archived psts. Training the end users in this process may help, it depends upon the skillsets of the user base. This is more of a process solution, then technical;but it will work. Document the process, train the users, help to move to PSTs. Be sure you can backup the PSTs, they are open files if Outlook is still holding them.