Exchange 2013 has two Roles:
- Mailbox Server Role
- Client Access Server Role
Each organization requires minimum one Mailbox Server Role and Client Access Server Role.
Mailbox Server Role Includes:
- Client Access Protocols
- Transport Service
- Mailbox Databases
- Unified Messaging (Except SIP Redirection)
- Handles all activities for active Mailboxes on that Server
Client Access Server Role Includes:
- Authentication
- Redirection (limited)
- Proxy Services for HTTP, POP, IMAP and SMTP
- Thin and Stateless Server
- Does not do any data rendering
- Nothing is queued or stored here (except diagnostic logging)