We currently are a Domino Shop with no Active Directory interaction. We are migrating to Exchange 2013 SP1 and have two Active Directory Forests with a two way trust. We have one email domain and MX record for the users on these two domains and need it to remain that way. Can FIM 2010 still be designed the same way between these two active directory forest?  We will have to put Exchange Servers on both LAN Domains due to a firewall constraint between the two AD Forests, but we want one centralized GAL.  Please advised the appropriate steps to accomplish this. Thanks, Margaret

Yes FIM 2010 can be used to synchronize between the two forests.

I would look at the GalSync Wiki