A. With Exchange Server 2007, if a mailbox server role is made highly available by being a member of a Single Copy Cluster or Cluster Continuous Replication failover cluster, no other roles can be installed on the mailbox server.

Exchange Server 2010 changes this. If an Exchange 2010 mailbox server is part of a Database Availability Group (DAG, the Exchange 2010 high availability solution), you can still install other roles on the Exchange 2010 mailbox server, even though it's highly available. Just because you can do it doesn't mean you should—in most implementations, you should still separate roles onto multiple servers—but it's an option.

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