I am using Microsoft Fax server with Brooktrout SR140 (sip fax provider) and t38fax.com and I am able to fax out just fine. When I try to register to the sip extensions on my Mitel 5000 the SR140 will dial out and the receiving fax answers but the faxes never connect. The Window Fax Server states "No Dial Tone" or "disconnected". I point back to t28fax.com and we are good again. Am I missing a configuration piece on the Mitel sip extension to allow faxing?
