Do you have their digital voice service? If not, tell how you hooked up your fax machine.
If you have digital voice it's known that some fax machines never work there. Try another model.
I have been having terrible problems sending faxes from my fax machine that is connected via Cox high speed broadband. I thought it might be a band width issue so I called Cox. They changed one setting that is supposed make analog fax machines and credit card modems more compatible with a digital system.
But I am still unable to send faxes on a regular basis. Sometimes I can get a couple of pages to go through and other times nothing will go through. I have tried two different fax machines at two different spots in the house and have not had any better luck. I receive all my faxes via efax and my email works perfectly so I don't have any problem there - just outgoing from my fax machine. I have tried faxing them to my efax account so I could email them, but I can't get that to work either.
I know I could scan everything in to a .pdf but I have sizeable outgoing faxes and it would require two separate operations.
Bottom line is - has anyone else had this problem and found an answer?