Today I had reason to report spam to Mailchimp (some of you are laughing already, I know). As I usually do, I forwarded the spam message we'd received to them as a message/rfc822 MIME part, with a prequel plain text part saying that it was spam. Forwarding email as a MIME message/rfc822 part is unambiguously the correct way to do so. It's in the MIME RFCs, if done properly (by the client) it automatically includes all headers, and because it's a proper MIME part, tools can recognize the forwarded email message, scan over just it, and so on.

So of course Mailchimp sent me back an autoreply to the effect that they couldn't find any spam mail message in my report. They're not the only people who've replied this way , although sometimes the reply says "we couldn't handle this .eml attachment". So I had to re-forward the spam message in what I called literal plaintext format . This time around either some human or some piece of software found the information and maybe correctly interpreted it.

I think it's perfectly fine and maybe even praiseworthy when email abuse handling systems (and people) are willing to accept these literal plaintext format forwarded spam messages. The more formats you accept abuse reports in, the better. But every abuse handling system should accept MIME message/rfc822 format messages too, as a minimum thing. Not just because it's a standard, but also because it's what a certain amount of mail clients will produce by default if you ask them to forward a message. If you refuse to accept these messages, you're reducing the amount of abuse reports you'll accept, for arbitrary (but of course ostensibly convenient for you) reasons.

I know, I'm tilting at windmills. Mailchimp and all of the other big places doing this don't care one bit what I want and may or may not even do anything when I send them reports.

(I suspect that many places see reducing the number of 'valid' abuse reports they receive as a good thing, so the more hoops they can get away with and the more reports they can reject, the better. In theory this is self-defeating in the long run, but in practice that hasn't worked with the big offenders so far.)