The multi-role server architecture that was introduced with Exchange Server 2007, and then continued with Exchange 2010, has been consolidated in Exchange Server 2013.
Exchange 2013 has three server roles that can be installed:
- Client Access server
- Mailbox server
- Edge Transport server (from SP1 or later)
The Mailbox and Client Access roles can co-exist on the same host, or be installed separately. It is generally recommended to install them on the same server (multi-role server installs) instead of separate server roles.
Exchange Server 2013 Client Access Server
As the name suggests, the Client Access server role is the server that clients (eg Outlook, Outlook Web App, ActiveSync) connect to for mailbox access. The Client Access server authenticates, and redirects or proxies those requests to the appropriate Mailbox server.
Client Access servers can be made highly available through the use of a load balancer.
There are two main components:
- Client Access service – this handles the client connections to mailboxes
- Front End Transport service – this performs various email traffic filtering functions, as well as email routing between the Exchange servers and the outside world
Exchange Server 2013 Mailbox Server
Mailbox servers host the databases that contain mailbox and public folder data. As with Exchange 2010 the Exchange 2013 Mailbox server role can be made highly available by configuring a Database Availability Group.
The Mailbox server also runs two Transport services:
- Hub Transport service – similar to the Exchange 2007/2010 Hub Transport server role, this service provides email routing within the organization, and connectivity between the Front End transport service and the Mailbox Transport service
- Mailbox Transport service – this service passes email messages between the Hub Transport service and the mailbox database
Exchange Server 2013 Edge Transport Server
Edge Transport servers are optional for organizations, and are designed to sit in a DMZ network to provide SMTP connectivity and mail flow in and out of the organization, whether to/from the internet or Office 365. The Edge Transport role can be used to satisfy the requirement that some organizations have to not permit any direct communications from the internet to internal networks.
Other Server Roles from Exchange 2007/2010
With the reduction in server roles to just two in Exchange Server 2013 you may be wondering what has happened to the remaining server roles that existed in Exchange Server 2007 and 2010:
- Hub Transport server – this functionality has been divided between the Client Access server (Front End Transport service) and Mailbox server (Hub Transport and Mailbox Transport services) and is no longer a dedicated server role
- Unified Messaging – this functionality has been divided between the Client Access and Mailbox server and is no longer a dedicated server role