As Exchange Server 5.5 gets ready to ride off into the sunset, the process of migrating Exchange 5.5 mailboxes to Exchange Server 2003 is taking the top spot on many administrators' to-do lists. Microsoft has an arsenal of tools, white papers, case studies, and other documentation that outlines the process of moving mailboxes, public folders, connectors, and other messaging objects to a new system (or even a new Exchange organization). Here are a few of the best tips that I've collected from migrations large and small.
You might have noticed that some of Microsoft's migration guidance recommends running the Directory Service/Information Store (DS/IS) consistency adjuster after you move mailboxes to Exchange 2003 machines. The consistency adjuster does a number of things, including removing bogus ACLs from mailboxes and ensuring that every directory entry in the Exchange 5.5 directory is linked to a mailbox and vice versa (the Microsoft article "XADM: Function and Effects of Running the DS/IS Consistency Adjuster," at http://support.microsoft.com/?kbid=182979 , more fully describes the adjuster's functions). Running the consistency adjuster is a good idea, but you should run it BEFORE you move mailboxes, not after--at that point, it's too late for the adjuster to fix much of anything.
An often overlooked tip is to clean up users' mailboxes before you migrate them. This task can be as simple as running the Mailbox Manager to clean out old junk. If your users are cooperative, you can ask them to archive some of their messages to .pst files (assuming that doing so won't violate your corporate retention policy). Once you've cleaned up the mailboxes as much as possible, you'll find that moving them will take less time, and the moved mailboxes will take up less space on the target servers. On a related note, you need to perform an offline defragmentation on the original server only when you're going to keep it around and need to immediately reclaim the space occupied by the moved mailboxes. If you're just going to decommission the server, don't worry about defragging it.
Speaking of decommissioning servers: Many migration schedules are front-loaded so that only a brief time is allotted to tasks that have to happen after the mailboxes and public folders are moved. Resist the temptation to just turn off your servers and dump them at the curb, though. Instead, make sure that you've successfully rehomed all your connectors and public folders--by shutting the servers down for a day or two, then checking to make sure that all your migrated mailboxes and folders work properly--before you permanently remove them from your old servers. Doing so gives you an easy recovery route if you run into problems--just turn your old servers back on.
I'm sure that as more customers get Exchange 5.5 migrations under their belts, we'll see new (or slightly revised) best practices from Microsoft. In the meantime, feel free to share your best practices for smooth migrations with me. I'll publish the best ones in a future column.