Legacy versions of Exchange 2007 and Exchange 2010 released with 5 server ROLES, ie, Mailbox, CLIENT Access, Hub Transport, Unified Messaging and Edge Transport server. Server ROLE architecture has been changed in Exchange 2013 which released with only two server roles.

Mailbox Server role: It holds the same function of Mailbox, the client access protocols, Hub Transport and Unified Messaging server role in Exchange 2010

Client Access Server role: work as the client access server role in Exchange 2010, Exchange 2010 work as only STATELESS server, where it doesn’t do any data rendering, and nothing will be stored or queued in Client Access Server role. CAS offers all usual client access protocols: HTTP, POP and IMAP, and SMTP

Legacy versions of Exchange 2007 and Exchange 2010 released with 5 server roles, ie, Mailbox, Client Access, Hub Transport, Unified Messaging and Edge Transport server. Server role architecture has been changed in Exchange 2013 which released with only two server roles.

Mailbox Server role: It holds the same function of Mailbox, the client access protocols, Hub Transport and Unified Messaging server role in Exchange 2010

Client Access Server role: work as the client access server role in Exchange 2010, Exchange 2010 work as only stateless server, where it doesn’t do any data rendering, and nothing will be stored or queued in Client Access Server role. CAS offers all usual client access protocols: HTTP, POP and IMAP, and SMTP