This post will serve as a ready reckoner to those who are looking to understand and implement Microsoft® Exchange Server® roles. Exchange Server 2007, 2010, 2013 have different architecture models when compared to the new 2016.

 

Server Roles in Exchange 2007 & 2010

There are five server roles in Exchange Server 2007 & 2010 as follows:

  1. Mailbox Server: Hosts the mailbox and public folder databases and also provides MAPI access to Outlook clients
  2. Client Access Server (CAS): Hosts the client protocols, such as POP3, IMAP4, HTTPS, Outlook Anywhere, Availability service, and Autodiscover service. CAS also hosts Web services.
  3. Hub Transport Server: responsible for all email flow in the organization, internal routing and policy enforcement
  4. Edge Transport Server: A special transport server intended for installation in DMZ networks to provide secure inbound/outbound email flow for the organization
  5. Unified Messaging Server: Provides VoIP capabilities to an Exchange Server in order to integrate e-mail, voicemail and incoming faxes as part of an inbox.

 

The Mailbox Role is generally installed along with the CAS, Hub Transport Server and Unified Messaging Server roles on a single server. The Edge Transport Server Role sits on the perimeter and is not part of AD.

 

Server Roles in Exchange 2013

Exchange Server 2013 consolidated some of the Exchange Server roles from 2007/2010. After Hub Transport server and Unified Messaging server roles were discontinued in 2013, it now has only the following server roles for installation as follows:

  • Mailbox Server: This server role hosts both mailbox and public folder databases and also provides email message storage. The Mailbox server role has 2 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

Mailbox servers can be added to a Database Availability Group, thereby forming a high available unit that can be deployed in one or more datacenters. DAG is the base component of the high availability and site resilience framework built into Microsoft Exchange Server 2013. A DAG is a group of up to 16 Mailbox servers that hosts a set of databases and provides automatic database-level recovery from failures that affect individual servers or databases.

  • Client Access Server: Exchange Server clients such as Outlook, Outlook Web App and ActiveSync connect to CAS for mailbox access. CAS authenticates, and redirects or proxies those requests to the appropriate Mailbox server. CAS has 2 main components:
    • Client Access Service: This handles the client connections to mailboxes
    • Front-end Transport Service: This handles all inbound and outbound external SMTP traffic for the Exchange organization, and can act as a client endpoint for SMTP traffic

The CAS role does not perform any data rendering functionality in 2013 and only provides authentication and proxy/redirection logic, supporting the client Internet protocols, transport, and Unified Messaging.

  • Edge Transport Server: Though this role was discontinued with Exchange Server 2013, the latest SP1 of 2013 has reintroduced this role. Edge Transport servers minimize attack surface by handling all Internet-facing mail flow, which provides SMTP relay and smart host services for your Exchange organization, including connection filtering, attachment filtering and address rewriting.

 

Server Roles in Exchange 2016

Exchange Server 2016 consolidated some of the Exchange Server roles from 2013. The Client Access Server role was consolidated with Mailbox Server role and the Edge Transport Server role has been introduced again. The reason for consolidating Client Access Server with Mailbox Server is to reduce the number of servers and cost of hardware. Separate server roles can result in long-term cost disadvantages as you may purchase more CPU, disk, and memory resources than you will actually use.

  • Mailbox Server: The Mailbox server role in Exchange Server 2016 is the only mandatory server role, and the consolidation reinforces the recommended practice since Exchange Server 2010 to deploy Exchange as a multi-role server instead of deploying individual roles to separate servers.
  • Edge Transport Server: This role will be much the same as Edge Transport in previous versions of Exchange, designed to sit in perimeter networks and provide secure inbound and outbound mail flow for the organization. Note: Edge Transport servers are not mandatory.

 

Exchange Server 2007 Roles

Exchange Server 2010 Roles

Exchange Server 2013 Roles

Exchange Server 2016 Roles

Mailbox Server

Mailbox Server

Mailbox Server

Mailbox Server

Client Access Server

Client Access Server

Client Access Server

Compared to Exchange 2010 and 2013, Client Access Server role is consolidated with Mailbox Server role.

Hub Transport Server

Hub Transport Server

Hub Transport Server functionality has been divided between the Client Access server and Mailbox and is no longer a dedicated server role.

Compared to Exchange 2010, Hub Transport Role is consolidated with Mailbox Server role.

Unified Messaging Server

Unified Messaging Server

Unified Messaging Server functionality has been divided between the Client Access and Mailbox server and is no longer a dedicated server role.

Compared to Exchange 2010, Unified Messaging Server role is consolidated with Mailbox Server role.

Edge Transport Server

Edge Transport Server

Exchange 2013 does not contain the Edge Transport server role.

Edge Transport Server

 

Learn More:

Find out how to discover, configure and monitor Exchange Mailbox Server using SolarWinds Server & Application Monitor: http://thwack.solarwinds.com/community/solarwinds-community/product-blog/blog/2013/12/18/appinsight-for-exchange

 

References:

  1. Microsoft Exchange Server News - Tips - Tutorials
  2. Resources and Tools for IT Professionals | TechNet
  3. Exchange Server 2016 Architecture | TechNet