Thanks for your response Mark.
I added the Reverse settings in DNS, which it sounds like I didn't need to do. Before adding this, I ran DCDiag and the error was that the DNS name could not be resolved. Other DCDiag tests seemed to run though.
Should I uninstall the Reverse DNS? If so, Do you know what I would need to do to get rid of the DNS name not resolving please?
Cheers