Inbound and Outbound MTAs

When Messaging Server hosts are each supporting many users, and there is a heavy load of sending SMTP mail, offload the routing task from the Messaging Server hosts by using separate inbound and outbound MTAs. You can further share the load by designating different MTAs to handle outgoing and incoming messages.

Often, both the inbound and outbound MTAs are combined as a single In/Out SMTP host. To determine if you need one or more MTA hosts, identify the inbound and outbound message traffic characteristics of the overall architecture.