Ah right, the aim here was to use Discourse’s Watched Word feature to automatically tag new topics based on the content of its first post (the question), and reject the mail if no special keywords were found. But I don’t recall testing that with emails so can’t say whether it works…
AFAIK Discourse does some mangling to prettify emails replies, such as removing PGP/MIME attachments, quoted messages at the bottom of top posters, etc. Replies arriving by emails are publicly marked as such (like for GitLab and GitHub AFAIK) — you can see an example here and while the styling might be slightly different (greetings etc.) I find the mangling pretty good.
Having the ability to reply by email has been a long-requested feature of our AskBot instance and I’m really keen to keep it now that we have it and that people started using it