Complex Exchange migrations, part 1

One fun thing about being where I'm at is that the previous IT regime was -- how shall I put this -- less than competent. That leaves me in the position of working with two forests and an Exchange 2003 implementation that likes to go down harder than a drunken baby in a roller derby. To fix this, I've got a plan of attack that involves migrating all of the users into the new, working, 2008 R2 functional level forest (we'll call it new.company.com) and onto a shiny new Exchange 2010 server (mail.company.com). Because this is a staged roll out that's happening at the same time as a Windows 7 implementation, we have to maintain coexistence and both forests for some time. That means that I'm doing a cross-forest Exchange migration from a legacy version, which is what I like to think of as "complex."

In the next posts on this topic, I'm going to walk you through how to pull this off in a mid-sized business. The basic steps are:

• Install Exchange 2010 in the new domain;
• Figure out how to synchronize the GALs for mail flow;
• Create cross-forest accounts and connectors;
• Script the movement of mailboxes;
• Clean up any messes that arise.

I'll assume you can figure out how to install 2010; it's pretty straightforward. I'll pick up with GAL synchronization and what exactly you need to create in the other domain to get mail working. I personally used ILM, but I know enough now about the schema to provide you with a PowerShell script to sync the GAL.