I recently had the pleasure of dealing with a customer who renamed their Exchange mailbox servers, and the pains that went along with it.  The obvious thing here is, you should never be renaming your Exchange mailbox servers, and I will attempt to explain why.  The first thing to realize is that Active Directory is liberally populated with references to an Exchange server name.  These are everywhere in Active Directory, so when you make this change, there is a good chance (100% certainty) that AD will not populate these changes to all the users.  So why is this a big deal?  Those settings in AD are the configurations that we use every single day.  When you make a change to the object that active directory references, AD has no way knowing the new name of the object.  This can cause you HUGE problems going forward with things like Remote-Powershell, Directory services, Calender delegates and many other LDAP objects.