Exchange 5.5 Backups

We have 8 branches in our company with an Exchange 5.5 server running on NT4.0 in each one.Management wants to be able to keep a daily archive of Exchange on each server so that they can go back and pull up any employee’s mailbox on any given day.Isthere a way to archive this info or a product that will do this.I also do not like the thought of restoring a whole server to recover one mailbox.Any help is greatly appreciated.