Intelligent Email Routing

Many modern companies of all sizes have operations in two or more countries and often have multiple points of connection to the Internet from their internal networks. Such companies typically use these points of connection as ingress and egress points for email flowing to and from their internal Exchange Server environment. Routing outbound email through the egress point that's geographically nearest the sender is typically a straightforward matter of using routing groups and connector costs (as the sidebar "Optimizing Outbound Email Flow" explains). Intelligently routing inbound email through an ingress point that's geographically near the intended recipient is more difficult. However, you can implement such a routing mechanism by using basic Exchange Server 2003 features.

Using Namespace Design to Optimize Inbound Email Flow
The simplest mechanism for optimizing inbound email traffic is to have some component of the email address indicate the geographic location to which a message should be routed while still on the Internet. For example, suppose that US-based employee Willie Nelson has the email address Willie.Nelson@us.cantaz.com. To optimize inbound email flow, publish a DNS MX record such that all messages that have the address component us.cantaz.com will be directed to the US mail relay mailrelay.us.cantaz.com. By doing so, email sent to Willie will be routed to him over the most efficient path to the SMTP connector geographically nearest him. Typically, this MX record will include the other ingress points as higher cost relays so that a failure at the lowest cost ingress point won't prevent successful mail delivery. (However, be aware that rerouting to a higher cost relay because of a failure causes mail routing to be suboptimal in terms of resource usage.) Similarly, each of the other location-specific MX records would be configured with backup mail-relay servers through the other locations. . . .