we have a parent domain named domain.local and we are introducing a child domain call child.domain.local. What is the best way to setup Exchange 2010 in the child domain so that users in the parent domain do not see the child domain user's email addresses in the GAL. We are currently in the design phase so any and all suggestions are welcome. The only criteria is that users in the parent domain must not see child domain users in the GAL. thanks in advance

You can wait for Exch 2010 SP2 which is due for release shortly, and you can use GAL segmentation/address book policies. This should meet what you're looking for.Sukh