The Message Transfer Agent (MTA) Stacks service in Microsoft Exchange 2000 Server and in Microsoft Exchange Server 2003 is primarily used to provide backward-compatible message transfer services between Exchange 2000 Server or Exchange Server 2003 servers and Microsoft Exchange Server 5.5 servers in a mixed-mode environment.
Why and When to disable the MTA?
In an Exchange 2003 cluster, there is only one Exchange Virtual Server (EVS) which hosts the MTA resource. The MTA on this EVS is responsible for transporting email to/from Exchange 5.5 servers and/or 3rd Party connectors for all of the databases hosted on the entire cluster. The MTA has a built in limit of being able to transport messages to/from a maximum of 50 Exchange databases. On clusters that have greater than 3 nodes, there is the potential to exceed the number of databases the MTA will be able to exchange messages with. E.g. An 8 node cluster has the potential to host 140 Exchange databases (7 active nodes x 20 databases per node). Manual steps described in KB 899302 can be used to increase the maximum number of Exchange databases the MTA can communicate with from 50 to 60 per cluster (this enables the 4 node/60 database scenario where the MTA Stacks resource is still required). Supporting more than 60 Exchange databases in a cluster was the impetus for the Exchange product group to test and support MTA disabled scenarios with Exchange 2003.
For the reasons outlined above, it is recommended to disable the MTA following the steps outlined in KB 810489 on Exchange 2003 clusters which host greater than 60 databases. Also, customers have asked to disable the MTA in their environments to reduce the footprint for security related attacks. This change in Exchange 2003 support, specific to running with the MTA disabled, satisfies both needs.
Microsoft does not recommend that the MTA Stacks service be disabled on Exchange 2000 Server. This action is not supported. The MTA Stacks service is a core operational component. You may experience unexpected behavior if you disable this service. In Exchange 2000 Server, the MTA Stacks service is required to correctly process mailbox moves and for other core functions.
These dependencies on the MTA Stacks service have been removed in Exchange Server 2003. The Exchange product group has thoroughly tested Exchange 2003 scenarios with the MTA Stacks service disabled as well as validating the scenario for several months in Microsoft IT’s production Exchange environment. Microsoft supports Exchange Server 2003 deployments in which the MTA Stacks service is disabled.
Manual steps are required to disable the MTA Stacks Service in Exchange 2003 environments. Reference KB 810489; for detailed instructions on disabling the MTA on both stand alone and clustered Exchange 2003 servers.
- What is the support stance for the MTA on Exchange 5.5? Exchange 5.5 uses the MTA Stacks service as the primary transport. It is not supported and not recommended to run Exchange 5.5 servers with the MTA Stacks service disabled.
- What options do I have if I am in a “mixed mode” environment (interoperate with Exchange 5.5 or 3rd Party Connectors) but plan to have Exchange 2003 Clusters with greater than 60 databases? There are three options:
i. Do not exceed 60 databases/cluster till after the Exchange 5.5 migration is complete. Follow the manual steps outlined in KB 899302 to increase the number of MTA supported databases per cluster to 60. Design the Exchange 5.5 to Exchange 2003 migration in such a way that the database count per cluster does not exceed 60 till the Exchange 5.5 migration is complete which will allow you to disable the MTA on the Exchange cluster (KB 810489)
ii. Create a dedicated MTA Admin Group and Exchange 2003 MTA bridgehead server. Create a dedicated MTA Admin Group and place an Exchange 2003 server to act as the MTA bridgehead in it. Configure Exchange 5.5 servers to route email to the Exchange 2003 environment via this Admin Group/Server.
iii. Reduce node count in Exchange cluster architecture: Change cluster architecture plans to be based around a 4 node cluster (as opposed to a 5-8 node cluster). Follow the manual steps outlined in KB 899302 to increase the number of MTA supported databases per cluster to 60. This will allow you to keep the MTA resource on the cluster and work with 60 Exchange databases (3 Active/1 Passive; 4 node cluster).
- What are the relevant KB articles related to this issue: KB 899302, KB 810489
- Is there any QFE or service pack required for Microsoft support of Exchange 2003 environments where the MTA is disabled? No, the support stance change does not depend on any Service Pack or QFE. The support stance has been changed based on recent Exchange product group testing where no issues were found running Exchange 2003 with the MTA disabled (after following steps outlined in KB 810489 ). The testing of this scenario was the validation that running Exchange 2003 with the MTA disabled was supportable.