Virtual Domains in Forefront Online Protection for Exchange
You can create virtual domains within FOPE to provide different filtering settings for a particular group of users, specify a different mail delivery location for a subset of users, and to rewrite recipients' email address based on the needs of your organization. This video will show you how to create and configure virtual domains.
Check this video out at: http://edge.technet.com/Media/Virtual-Domains-in-Forefront-Online-Protection-for-Exchange/
Cheers,
Anderson Patricio
http://blogs.msexchange.org/patricio
Twitter: @apatricio