That's extremely kind of you. Please don't go out of your way, at all. I did make a little progress after I posted. We're coming from a .local domain, so I added UPN suffixes for .com, and set that on all AD user accounts. I ran a tool called IDFix and, sure enough, that identified a couple of mysterious system mailboxes with the .local UPN. I'm thinking that uninstalling Exchange on the server will do the trick, but that seems like it's not as easy as an Add/Remove Programs thing, and might require some powershell for the Exchange DB and system mailboxes. I'm thinking the uninstall will fail, but it'll throw up errors that show why, and lead to the solutions.That's about where I stopped today. If you have some tips and possible gotchas, I am so all ears. Thanks a lot!