How to share a single e-mail domain between two or more Windows Small Business Server 2008 servers is a technical document that was recently made available to download.
Brief Description
Outlines the steps necessary to share a single SMTP domain between two or more Windows SBS 2008 servers
Overview
This article written by Microsoft Support Engineer Edwin Joseph discusses the process you should follow to share a single SMTP (e-mail) domain between two or more Windows Small Business Server 2008 (Windows SBS 2008) servers that reside in different active directory domains.