Hi Kirchie, Exa are a very friendly ISP and should be able to help discuss this further directly.
In the meantime please be aware that the sendlogon executable mentioned expects to talk to a Bloxx Proxy - the port that is mentioned 3898 in the documentation is a custom port - not an Active Directory server port.
Exa have the ability to use your internal IP addresses and Active Directory usernames and groups to apply filtering rules with SurfProtect as long as an ICAP compatible appliance is present on the network to make the request to Exa's proxies.
Please call Exa Support on 0845 1451234 and ask to speak to Mark in Technical who can discuss this further :-)