I only started experiencing the problem in December. The problem seems to be only if your IP address has been associated with a spambot virus. As BTL uses dynamic IP addressing you can end up with an IP address that someone else was using who may have had a spambot on their system. I've checked my system fully and have no issues with any kind of virus so that's the only explanation I can think of. You can request removal from the blacklist database and within a few minutes Spamhuas will try and infiltrate your system, if they can't you come off the blacklist.

It's also only sending TO COMCAST addresses. I had been receiving e-mails from clients asking why I hadn't confirmed their orders (when I had repeatedly.) That was when I did the research and found out the problem.