Can some one please help with the following question? I am thinking of the following strategy for migrating to AD. Please comment on it's feasibility. We have a single NT domain with an Exchange 5.5 server. I was thinking of two scenarios: 1) Set up a separate AD domain and Exchange 2000 server. I'm thinking that it's possible to setup a one way trust relationship between the NT and AD domains. Is it possible to synchronize the exchange 5.5 and 2000 servers accross the two domains? I'm thinking that to sync exchange servers they have to belong to the same site, but if I build the Exchange 2000 and give it the same site name as the Exchange 5.5 would the sync work or do I have to establish the trust relationship first then join the Exchange 2000 to the Exchange 5.5 site? I want to maintain parallel domains so that if there will be major AD problems several months down the line after the migration I can revert to the old NT domain and still get an up to date email server. 2) The second scenario is to not maintain parallel domains. My concern is that if we have to roll back to the NT domain after spending a few months running the Exchange 2000 server I will not be able to rebuild the Exchange 5.5 using the Exchange 2000 databases. I've rebuilt an Exchange 5.5 server using just a backup of the Exchange 5.5 dir.edb, priv.edb and pub.edb databases before, but knowing that Exchange 2000 does not have its own directory database but rather uses the AD as its directory source, I don't think I can rebuild the Exchange 5.5 using the Exchange 2000 data. Or am I wrong about that? This is definitely a test network first thing but I just want to get some opinions and insights before I dive into setting up a test network and find out that it's not possbile. Appreciate all the help.