The RPC Client Access (RPC CA) service is enabled by default when you install the Exchange 2010 CAS role. The RPC CA service handles the Outlook MAPI connections.

The change in Exchange 2010 to move all processing to the CAS was implemented to provide all data access through a single, common path of the CAS. This change improves consistency for applying business logic to clients, and provides a better client experience when failover occurs. This change also allows a higher number of concurrent connections per server and a higher number of mailboxes per server.