According to the document below, I should be able to set up one Unified Messaging service to access mailboxes on both Exchange 2010 and Exchange 2007 servers. I setup my service to point to 2010 CAS servers and I can access 2010 mailboxes, but testing 2007 mailboxes comes up with an http 200 error. If I setup the CAS server as 2007, I can access 2007 mailboxes, but get an error on 2010 mailboxes. This will be a real pain if I can't do this with one service. I don't want to have to keep Unity Connection updated as users get moved from 2007 to 2010! Anyoe know how to do this?