I am using Microsoft Small Business Server and have set-up NT Fax Server to send faxes. The modem is US Robotics Voice 56K and is shared by other services for RAS and email. It works perfectly for these but refuses to connect with a FAX.
It dials out OK rings once then hangs up claiming that the line is busy. This is a load of bolicks as it does the same thing if I dial a number that I know is not busy and has no FAX attached. I have confirmed that the phone of the number it dials rings briefly. I suspect it is not waiting long enough for the FAX to answer.