Thanks for the great post which explains why my Exchange install on R2 is failing. It’s pretty unbelievable that Exchange 2007 won’t be supported on 2008 R2, but recalling the feature-incomplete product the Exchange team dumped on us prior to 2007 SP1, it should come as no surprise that they are basically ambushing Exchange admins everywhere with this surprise. What hidden gotchas can we expect in Exchange 2010, I wonder.
Speaking from experience now, Exchange 2007 SP1 passes all prerequisites on 2008 R2 RTM, begins to install, fails halfway through the Mailox role portion, refuses to uninstall, leaving a broken half installed copy of Exchange that cannot be removed. Nice job Microsoft!