For a front end server to make any sense, a minimum of three servers would be needed: the front end server itself, and at least two Exchange servers, to which the front end server would route messages, based on the mailboxes homed on each. In our migration scenario, one could have a front end server routing mail to the old Exchange 2000 server and the new Exchange 2003 server. As mailboxes are moved from the old to the new server, the front end server would route messages to the correct place. This is a nice option for those with the hardware and the desire to do a gradual transition.