I have an Exchange Server site running now. I want to replace the server with a new one but with very little down time. I started installing exchange 5.5 on the new server and it asks if I want to join an existing site or create a new one. Can I join the existing site, if so what happens when you do so, does it take all of the user's mail boxes, and transfers them to the new server or does the new server act as a backup. What will happen when I take the primary server offline, does the new server take over. Any help or guidance appreciated, I aml trying to limit the suprises.