Identified internal IP as source

[FranklinCat]

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

[gnarlymarley]

1 hour ago, FranklinCat said:

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.

That sure is a lot of received lines.  From what I can see, the source appears to be a fastmail user.  SpamCop is really good at detecting company to company connections, but RFC9181 IPs can be assigned to every company.  The source of 10.202.2.71 will need to be looked at by a fasthost admin, which is why SpamCop gives you the message "identified internal IP as source".

[FranklinCat]

OK.  I do report all these phishing attempts claiming to be from FastMail directly to FastMail, but I'll send them a query to see if they have anything to say about this.  Thanks!