> just forward ... with a reporting account
I'll look into what a "reporting account" is.
It is just an account with Spamcop.net. I log in, and I am shown a text field for the copy and paste.
Now, I dunno. A few years ago I tried reporting mail forwarded from an address@spamcop to one @sonic -- and Spamcop automatically tagged Sonic as a spam-friendly ISP.
Spamcop.net recommends configuring mailhosts; indeed, without doing so, much reported spam will not even generate a report. A "mailhost" configuration is created by requesting a test email to be sent to the email address for which you will be reporting spam. The test email is received at your email address, and you enter it in the SC parser. This email includes a code, so the SC parser knows it is not spam. From the test email headers, and the test code, Spamcop.net learns what your normal inbound path looks like. This avoids errors, such as you experienced.
Once the account is set up, you can get a customized reporting email address; something like, "submit.%Rnd_Chremail@example.com". Using this, you can forward spam "as an attachment". When the spam has been processed, you get an email from "SpamCop AutoResponder" with this Subject: "[SpamCop] has accepted 1 email for processing". Inside is a link to the reporting page.