Having TWO server roles with MAILBOX Server includes all the traditional components fount in Exchange 2010: the client access protocols, TRANSPORT service, mailbox databases and unified messaging and the Client Access Server role to provide authentication, limited redirection and proxy services.

New architecture provides the below benefits:

1. The Client Access Server and Mailbox Server become “LOOSELY COUPLED”. All process and activity for a specific mailbox occurs on the mailbox server that holds the active database copy, eliminating concerns of version compatibility between CAS and Mailbox Server
2. Version Upgrade flexibility – Client Access server can be upgraded independently and in any order.
3. Session affinity to client access server role is not required – In Exchange 2013, Client access and mailbox components available on the same mailbox server, because the client access server simply proxies all connections to a specific mailbox server, no session affinity is required
4. Only two namespace is required for Exchange 2013

Having two server roles with Mailbox Server includes all the traditional components fount in Exchange 2010: the client access protocols, transport service, mailbox databases and unified messaging and the Client Access Server role to provide authentication, limited redirection and proxy services.

New architecture provides the below benefits: