I read a lot of documents about Unity with multiple exchange servers but fail to set it up. I have Unity 5.0.1 partner with an Exchange 2003 back-end server. I run permission wizard and allow Unity to see all the other back-end Exchange servers. I then create a subscriber and at the bottom I select another Exchange server. When I log into Unity, Unity promps play message "Message server is not available". Unity works fine with the Exchange server that I partner with. Am I doing something wrong?