This post is focused on those of you who have decided to deploy Exchange in a resource forest.  You’re in for tears.  While the resource forest is technically a supported deployment method for Exchange, I’m going to point out what can go wrong in your Exchange world that will keep your admins up at night.
Let’s start with the definition of a resource forest, just in case you’re not sure.  The resource forest approach means that you have one Active Directory forest where your user accounts live and another Active Directory forest where your application (Exchange, in this case) lives.  You have user accounts in the resource forest that are disabled and then externally associated with the users in the user forest.  This of course, requires a trust between the two forests, which you likely have anyway, right?  Right.
