WTF Earthlink

Some user of a program of mine reported a bug a couple of days ago. I fixed the bug and told him about it. Then he had another question, I responded but now this came back:

<*****@earthlink.net>: host mx3.earthlink.net[209.86.93.228] said:
550 IP 78.47.130.37 is blocked by EarthLink. Go to earthlink.net/block for details.
(in reply to MAIL FROM command)

Since I'm operating my own mailserver I'm pretty sure it doesn't send spam mails to anyone let alone Earthlink. Don't get me wrong, my own anti spam policy is pretty radical. But putting an ip address on a block list for ONE message? What the fuck is wrong with you guys at Earthlink?!

So, how shall I respond? Beg them to delist my ip address? Why shall I do anything in the fist place anyway? Nope, won't do that.  Fix your friggin' stupidity yourself, Earthlink. Your mailservers are being blocked by mine as well now. But at least you've got an advantage over me: you know why you're being blocked. On the other hand - I block everything from you, including complaints.

Too bad.