Just got a bit closer to resolving the email situation [1] (yes, it's still in the process of being resolved two weeks after it started). I just now received a call from AbuseBob, who works for the Abuse Department at The Monopolistic Phone Company. Nice guy, and he confirmed that not only is the one server being blocked, but that another server our customer has has also sent spam. He would like to work with us, but we need to make sure we're filtering spam before it gets sent to The Monopolistic Phone Company email servers.
But more importantly—I have AbuseBob's phone number!