A. If a mailbox server is part of a high availability group in Exchange 2007, the server can't host the CAS, Hub Transport, or any other role. With Exchange 2010, you can have a single server hosting CAS, the Hub Transport role, unified messaging, and a mailbox server as part of a DAG. Of course, in most scenarios you wouldn't want to co-host these roles for performance reasons, but it is now a possible combination.

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