A. Microsoft has changed its stance about disabling the MTA on Exchange Server 2003. In Exchange 2000 Server, you couldn't disable the MTA, but because of limitations with the MTA in cluster environments and because its primary use is for communicating with Exchange 5.5 servers, Exchange 2003 lets you disable the MTA. The main problem with maintaining the MTA is that in a cluster, only one Exchange Virtual Server hosts the MTA resource, which is responsible for all mail transportation to Exchange 5.5 servers or third-party connectors for all databases hosted on the entire cluster. But the MTA can communicate with only 50 databases (60 with a change to the system; see the Microsoft article "How to increase the number of databases that are supported by the MTA service when Exchange Server 5.5 coexists with a server cluster that is running Exchange Server 2003" at http://support.microsoft.com/?kbid=899302 ). Because each node in a cluster can host 20 databases (five database over four storage groups), if you have more than three active nodes the MTA can't communicate on behalf of all the databases in the cluster. For more information about disabling the MTA, see the Microsoft article "MTA Stacks service supportability guidelines for Exchange 2000 Server and Exchange Server 2003" http://support.microsoft.com/?kbid=810489 . If you don't require Exchange 5.5 communication or third-party connectors, and you want more than 60 databases in a cluster, you need to disable the MTA.