I have been using FastMail as my primary email since Spamcop ended its email service. Starting a couple weeks ago, when trying to report phishers, trying to get me to reveal my login for Fastmail, I'm faced repeatedly with the following response from Spamcop:
"Mailhost configuration problem, identified internal IP as source
..........
No source IP address found, cannot proceed."
Most of the rejected submissions had supposed return paths of <****@fastmail.fm>, and I suspected that may have had something to do with the problem, but this one had <watersh@mcmaster.ca> as its return path.
Is there something I can check for and tweak in the submission that will avoid the problem? I submit using my submit......@spam.spamcop.net address including spam as attachment.
https://www.spamcop.net/sc?id=z6633420934zc4b80047832b0517c88c3b8fb950b1d6z