Spamhaus and other rbl's have decided to not accept queries from public dns servers. There's a way around this if you have UT as one server and another server handling network dns. You point UT's dns to your isp dns. That way the spamblocker works correctly. You then have your network server(AD, or some other SSO system) use opendns or whatever public dns you wish. This allows you to have the spamblocker work correctly AND you can use opendns(as another layer of security or just for dns performance) of google or whatever public dns you want to.