The system is working correctly. The only way for the SBX to know if the call is a fax, is for a CNG tone to be present. If the senders machine is not sending the CNG, then it will never work right.

The only work other work around is to program the line to ring directly to the fax machine. Of course this sends all non-fax calls to the machine as well.

It goes without saying, but it is always best to have a dedicated fax line.