I believe this would have been the Hostname setting in Settings>General Settings (or thereabouts.) Alternatively you might find this in the protocol or port/binding settings as well as we allow configuration of that at multiple levels. Another thing Google has been harping on lately is ensuring your identified hostname matches the hostname in your IP address PTR (reverse DNS) record, so you might check that while you're in there too. I hope that helps!
Kyle Kerst
IT Coordinator
SmarterTools Inc.
www.smartertools.com