Perhaps someone can help me find an answer to a question I haven't been able to find yet. Here is the scenario. We have 2 Data centers one named A and the other B(backup datacenter). In Data center A we have an Edge server sitting in the DMZ. We have a second server with the Hub Transport and Client Access roles on it. Our third server is the mailbox server. We have the exact same setup in Data center B as we do A. The mailbox servers are setup using CCR. I know that the mailbox role requires a Hub Transport server in the same AD site. But the question is that if the Hub Transport server is Datacenter A should experience any failure will the exchange system then reroute through the Hub Transport server sitting in Data center B? Everything that I have read indicates no however I find this very difficult to believe. Can anyone shed some light on this?