Understanding Exchange Server 2007 Server Roles

Exchange 2007 introduces a new Exchange term: “Server Role”. Server role is a logical concept used to organize Exchange 2007 services and features across one or more servers. While Exchange 2003 provided primitive server roles called BackEnd server and FrontEnd server, Exchange 2007 has more granular divisions.


Dividing Exchange features among several server roles has advantages:

  • More flexible deployment topology: For a small or medium company that has only hundreds of mailboxes and all users are centralized, customer can install all required roles on one physical server. For a large enterprise where tens of thousands of mailboxes span multiple physical locations, customer can choose to deploy each role on a separate server or even multiple servers per role to provide better performance and fault tolerance.
  • Better hardware utilization and scalability: Because each role only installs binaries and runs services for a specific feature set. Unlike older versions of Exchange, configuring a server that has only one or two roles will reduce Memory, CPU and disk space requirements for this server. In addition, roles are scalable so admin can load balance work of one role to multiple servers.
  • Easy to maintain: Upgrading, applying hotfix, or other server changes that could cause server outage can be isolated to one server role. This reduces maintenance down time and end user impact. Admin can also install or uninstall roles on a server as needed.

So what are these roles anyway? During the beta releases of Exchange 2007, there were 6 planned roles. They were: Mailbox, Public Folder, Client Access, Edge, Bridgehead and Unified Messaging. As Exchange 2007 development progressed, Public Folder role was merged into Mailbox role since they share Extensible Store Engine and MAPI access. Additionally, “Bridgehead” role was renamed to “Hub Transport” to more clearly illustrate its functionality.

At Exchange 2007 release, the server roles will be:

  • Mailbox (MB): The Mailbox server role is responsible for hosting mailbox and public folder data. This role also provides MAPI access for Outlook clients. Note that there is also a variation of this role called Clustered Mailbox role, for use with high-availability MSCS clustering of mailbox data. When Clustered Mailbox role is selected, other server roles cannot be combined on the same physical server.
  • Client Access (CA): The Client Access server role provides the other mailbox server protocol access apart from MAPI. Similar to Exchange 2003 FrontEnd server, it enables user to use an Internet browser (OWA), 3rd party mail client (POP3/IMAP4) and mobile device (ActiveSync) to access their mailbox.
  • Unified Message (UM): This role enables end users to access their mailbox, address book, and calendar using telephone and voice. IP-PBX or VoIP gateway needs to be installed and configured to facilitate much of the functionality of this server role.
  • Hub Transport (HT): The Hub Transport role handles mails by routing them to next hop: another Hub Transport server, Edge server or mailbox server. Unlike Exchange 2003 Bridgehead that needs Exchange admin defined routing groups, Exchange 2007 Hub Transport role uses AD site info to determine the mail flow.
  • Edge Transport (ET): The last hop of outgoing mail and first hop of incoming mail, acting as a “smart host” and usually deployed in a perimeter network, Edge Transport provides mail quarantine and SMTP service to enhance security. One advantage of this role is that is does not require Active Directory access, so it can function with limited access to the corporate network for increased security.

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