Exchange Server 2003 can be configured to run without the Microsoft Exchange MTA Stacks service. In this configuration, if ...

{4}: Exchange Server 2003 can be configured to run without the Microsoft Exchange MTA Stacks service. In this configuration, if a message was found to require this service for routing, this delivery status notification is returned to the sender. Troubleshooting: Check your routing topology. Use the WinRoute tool to make sure that the routes are correctly replicated between servers and routing groups.