I have a site that is part of a geographically dispersed WAN. This site includes an Exchange 2003 Server that is part of an exchange organization that spans across this WAN (actually 1 other exchange server at another site). The client at this site would like to sever their ties to the shared AD Forest in the WAN. This will include an Active Directory restructure to a new forest and domain. The AD restructure can be performed by using ADMT to migrate objects. However, I am uncertain how to migrate the user mail stores and the exchange server. Everything I read suggests that you can only move mail stores between servers in the same exchange organizational group or must mimic your exchange org structure on a new server (same org name, admin groups, etc....).
Is there any well-defined way to migrate exchange mail stores across a forest trust to a new exchange server in a separate exchange org? The user base is fairly small (approx 40 users) - I guess if I absolutely had to I could export mailboxes to .pst and import back into new mailboxes in the new server. However that would be a last resort as it would entail the loss of rules, etc... in that exchange profile. Any assistance would be greatly appreciated!!