I have 2 separate organizations, domains, and forests. They are are linked together by a domain trust. As of yet I do not have a federated trust between exchange servers. Eventually these 2 organizations will merge into one organization. Basically one will for the most part absorbed the other. Many users of the one organization will be absorbed into the other organization while others will stay with the old organization. This will include mailboxes. I want to know if there is a way I can use the Exchange server of the old organization to host old email as well as set up a database etc for the new organization. basically I would like it to do firstname.lastname@example.org and email@example.com. Basically I want to continue to use as much of the old infrastructure as possible but transition it to the new company/new domain. I would like to set them up independently, but part of the same domain. Similar to having an office in NC and an office in MI all part of teh same domain but connected by MPLS. The great thing about the old organization is that it is across the hall and connected by Ethernet cable. I know this is somewhat vague as I am not sure how to put into words what I am envisioning.