I have a client who recently decided to migrate from GroupWise to Exchange 2013. During the course of the roll-out a few glaring compatibility issues became apparent and they decided to remove Exchange 2013. They are actually having problems even doing that, but that is another post.
The question is... Now that the AD schema has been extended for Exchange 2013, can they install a clean Exchange 2010 server in their environment or has the damage been done? There are no other Exchange servers in the environment.