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Exchange Admin 101: Server roles in Exchange Server 2007

Exchange Server 2007 introduces a role-based architecture that simplifies deployment and improves email performance and security. In this tip, you'll get a basic overview of the five server roles in Exchange Server 2007: the Client Access Server role, Mailbox Server role, Hub Transport Server role, Unified Messaging Server role, and Edge Transport Server role.

One of the major new differences between Microsoft Exchange Server 2007 and previous Exchange Server versions is a shift to role-based deployments. These server roles define the specific tasks that the server is intended to perform for the Microsoft Exchange Server organization.

Microsoft originally introduced the concept of server roles in Exchange 2000 when it first allowed for separate Exchange front-end servers and back-end servers. In Exchange Server 2007, and in many of the other new Microsoft products coming out, server roles are much more prominent and specific though.

The benefits of Exchange 2007 server roles

Server roles simplify deployment. During the Exchange Server 2007 installation process, you're asked which roles should be assigned to the server. When you choose a server role, Exchange 2007 Setup will install everything that is necessary for the Exchange server to fulfill that role. That means you don't have to go back later and manually install a bunch of subcomponents.

Being able to pick and choose Exchange server roles also ensures that no unnecessary Exchange Server components are running on your server. Eliminating needless components typically improves Exchange Server's performance and security.

There is a law of computing that states that the larger the code base running on a machine, the greater the chance that it contains exploitable security vulnerabilities. Assigning only the necessary server roles prevents any unnecessary code from being installed on the Exchange Server, thus keeping the size of the code base to a minimum.

Another advantage to role-based architecture is that it allows your Microsoft Exchange Server organization to be modular. Small companies can assign roles in a way that allows a single Exchange Server to perform all of the necessary tasks to meet the company's Exchange Server needs. Larger organizations can distribute roles across multiple servers to avoid overburdening any individual server.

There are five pre-configured server roles in Exchange Server 2007:

The Client Access Server role

The Exchange 2007 Client Access Server role is similar to the front-end server role found in Exchange 2000 Server and Exchange Server 2003. Its job is to provide the Outlook Web Access interface and to act as a proxy between Web-based clients and back-end Exchange servers.

The Mailbox Server role

The Exchange 2007 Mailbox Server role is fairly self-explanatory. Exchange servers running the Mailbox Server role host the databases used to store Exchange Server mailboxes. Just as in Exchange Server 2003, these databases can be clustered if necessary.

The Hub Transport Server role

The Exchange 2007 Hub Transport Server role has two responsibilities. First, it controls message routing. This is true whether an email is being routed between two mailboxes on the same Exchange server, or between multiple Exchange servers.

The Hub Transport Server role's second job is to enforce messaging policies for email being sent between recipients inside and outside the Microsoft Exchange Server organization.

The Unified Messaging Server role

Unified messaging is completely new to Exchange Server 2007. The basic idea behind the Unified Messaging Server role is that it allows Exchange Server to interface with compatible PBX systems. This allows voicemail and fax messages to be deposited into and accessed from Exchange Server mailboxes.

The Unified Messaging Server role also provides a component called Outlook Voice Access (OVA). OVA lets users access their mailboxes using a telephone. Using OVA, it is possible for users to telephonically "read" and compose email messages, and to manage their calendars.

The Edge Transport Server role

Earlier, I mentioned that a single Exchange 2007 server could host multiple roles. The Edge Transport Server role is the one exception to this. The reason is that servers running the Edge Transport Server role are intended to be placed in your organization's DMZ. The Edge Transport Server's job is to filter spam and viruses from inbound messages before they reach your perimeter network.

About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Exchange Server, and has previously received Microsoft's MVP award for Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at

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Related information from

  • Tutorial: A primer on Exchange 2007 server roles
  • Tip: Preparing for Exchange Server 2007
  • Tip: What to expect in Exchange Server 2007 Service Pack 1
  • Step-by-Step Guide: Test driving Exchange Server 2007
  • Reference Center: Exchange Server 2007 news, tips and resources

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