To my opinion, there is only one possibility to solve your problem : Use WSPCFG.INI files on your mail server! This .ini file has to reside in the same directory of your mail application. It can instruct ISA to listen to certain ports and to certain Nics. Look on technet for instructions (search for 'wspcfg.ini'). example: [MailProg] NameResolutionForLocalhost=P -> it uses proxy to resolve 127.0.0.1 LocalBindTcpPorts=25,110 -> open ports 25,110 on local NIC RemoteBindTcpPorts=25,110 -> open ports 25,110 on internal NIC of ISA ServerBindTcpPorts=25,110 -> open ports 25,110 on external NIC (not LAT) KillOldSession=1 -> if new session is due, kill old one Persistent=1 -> Keep open at all times (u need for inbound connections) Playing with these options you can try different solutions and pick the one which suits best in your situation. Try to simulate comms with telnet on port 25 & 110. Success ;-) Frederik