Microsoft Exchange 2007 was segmented by a number of different roles: Mailbox Server, Client Access Server, Unified Messaging Server, Hub Transport Server and Edge Transport Server. Although it’s not the end of the world if you install the roles in the wrong order, installation goes much smoother if you install Exchange 2007 server roles in a specific order.

If your organization small enough that you can deploy Exchange 2007 to a single server, then the installation order isn’t as critical. This strategy does apply, however, if you are using a multi-server Exchange 2007 infrastructure.

Here’s the best practice to use when determining role installation order:

  1. Client Access Server: Preps the environment for users to use the new services.
  2. Hub Transport Server: Required for most inter-role and inter-server communication.
  3. Mailbox Server: Holds mailboxes, but in order to access or handle mail, requires that a Client Access Server and Hub Transport Server be in place.
  4. Unified Messaging: Depends on all of the other roles to do its work.

The Edge Transport Server is not included in this list since it stands alone and cannot coexist with any of the above roles. If you do decide to use an Edge Transport Server, it’s best to install this role after you have a functioning Hub Transport Server since these two systems will be intertwined.