It appears that this list is sending its outbound traffic via Amazon's cloud operation.
This is a profoundly horrible idea, not through any fault of yours, but because Amazon's cloud operation is a massive, non-stop fountain of spam and Amazon personnel flatly refuse to lift a finger to do anything about it. As a result of this incompetence/negligence, some folks out there have taken defensive measures which may include firewalling, blocking, discarding, rejecting, etc. Thus this is not someplace that you want to try to send mail from if you really care about having it delivered. I recommend moving it elsewhere. And I'm perfectly willing to assist with that (either selecting another location or facilitating the move or both). ---rsk
