But wait, it gets worse...
The headers in the complaint that mailchannels.net sent me show the recipient's email only in coded form. i asked if it matched the address that I suspect is complaining and I got this reply:
"We unfortunately cannot reveal who complained or rejected your email. If you receive this type of rejection from us, it's possible you did nothing wrong. Email recipients frequently complain about legitimate messages."
THIS IS CRAZY! They are blocking emails because of a complaint that they know may not be legitimate and will not lift the block until the complaints stop for a period of time, but they will not say who the complaints are coming from so we can stop sending them email.