I've got a USN rollback issue resulting from installation of a new drive imaged from the old drive. So my two DCs are not replicating. I am wondering if this is the only reason exchange is not creating a mailbox when I add a user in AD on the exchange server? To clean up the USN rollback requires DC demotion, metadata cleanup, and then AD re-install,from what I have learned. Will this pose a problem with exchange? Thanks in advance.

This is actually two different issues. First issue is resolved - Exchange 2k3 Standard default database limit of 18gb was reached so it wouldn't create the new mailboxes. Made necessary registry changes and we're good to go. Second issue is a replication issue that I'mworking on with MS Support.