Sorry for the late response mgere, I was out of town on Friday. Before I left (Thursday afternoon) I switched our fax server back to using POTS lines. In my testing Thursday night and the ensuing fax logs it looks like I've gotten far fewer of these errors, so I think I can consider a major source of the problem as trying to run our fax server through the phone system.

As for the errors I'm still seeing, I'm not sure on the carrier used on all numbers where we're still seeing the errors, but I do know that most of what I'm seeing now is errors faxing to our internal fax machines.

In short, I've seen the enemy and he is us :^). I'll check with our vendor to see if there's anything I can do to address issues running fax machines through our phone system. I may contact our carrier if that proves unsuccessful.

Sometimes you carpe diem, sometimes your diem gets carped.