Hi, My company has a small affiliate company that's on its own AD forest and own Exchange organization. I've been asked to move the affiliate users' mailboxes over to our Exchange organization (separate forest, separate organization). I can accomplish this any way that I want - move only the mailboxes and keep their AD intact, or merge their AD onto our AD infrastructure. The only requirement is to keep some of their servers (file, app, database) at their current physical location. But other than that, I have free reign to recommend what I see as the best solution. The two approaches that I'm thinking of are as follows - 1) migrate only their mailboxes to our Exchange (Exch Migration Wizard) and keep their AD intact, and 2) merge the two domains by migrating user accounts (ADMT) and mailboxes (Migration Wizard), and create a new AD site for them (they're on a separate subnet). I'm assuming that the disadvantages of the first approach would be the requirement to set up external domain trusts, and associated external accounts have to be maintained for the users to access their mailboxes in our forest/organization. But what would be the advantage, if any? I can't think of why anyone would choose to go this route if they have the approval to just merge the two domains (and I have that approval). Are there any drawbacks to merging the two domains? I know it's a bit more work up front, but I can't think of any sustaining disadvantages of doing it this way. And what would the procedure be, at a high level? I'm assuming that the initial steps would be like this - a) migrate user accounts with ADMT, b) migrate mailboxes with Migration Wizard, c) demote their domain controller, d) update DNS. I'm sure I'm missing some steps here; can anyone fill in the gaps for me? Also, will the ADMT also migrate group, computer, and other objects, or am I off track on this, and I'll have to come up with another way to merge the two domains? Thanks in advance for any guidance or insight....

Option 2 would be your best bet for any time of domain collapse. Yes, ADMT will migrate computers, security groups, servers etc. It can not migrate Exchange Servers though so you will need to exmerge out and back in.Be careful with any servers running with service accounts, those will need to be updated once the server is migrated over to the new domain etc.There is a lot of useful information out there on migrating AD and Exchange from one domain to another. The process for Exchange may differ depending on what your coming and going to.SF - MCITP:EMA, MCTS

I would prefer the method 2 as well, which would make the IT management more centrally During the transition, you may need to keep the synchronization of Free/busy and replication of public folder between two forests Resources: Active Directory Migration Tool v3.0 Active Directory Migration Tool version 3.1 (For windows server 2008) ADMT v3.1 Guide: Migrating and Restructuring Active Directory Domains Exchange 2007 Cross Org Mailbox Migration How to Configure the Availability Service for Cross-Forest Topologies Installing, configuring, and using the InterOrg Replication utility Configuring Interorg Replication Tool for replicating the Public Folder & Schedule Free Busy between the forests Configuring Interorg Free/Busy between a single server Exchange Server 2007 organization and another forest Configuring Schedule+ Free Busy information between the forests Exchange 2007 & 2003