[pepve]

> Fastmail also has different actions for marking as spam and reporting phishing; I'm not sure how effective the latter is, but of course Thunderbird doesn't support it, as presumably that's a Fastmail-proprietary thing.

I don't think there's anything proprietary going on, so I did a quick search. Fastmail supports JMAP [0], and JMAP [1] supports setting special keywords [2] for a message to mark it as spam of phishing. It may be possible to get this to work.

[0] https://www.fastmail.com/dev/

[1] https://www.rfc-editor.org/rfc/rfc8621.html

[2] https://www.iana.org/assignments/imap-jmap-keywords/imap-jma...

[kelnos]

Ah interesting. Looks like that's strangely specific to JMAP and not a generic mail header or something like that, so K-9 won't be able to do it, as it doesn't (yet) support JMAP.