Please see my comment in your other question:-
http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Mdaemon/Q_24896489.htmlIn Setup, Default Domain & Servers, what is Domain IP set to? Try changing this to 127.0.0.1. Untick the box which says Restrict Connections to this IP.
If that doesn't do the trick, check your Firewall is not somehow blocking the 2nd NIC connection.