There doesn’t seem to be any way to find extensions for Mac Mail. There’s a Safari section in the AppStore, but nothing for Mail. I can search for “mail extension” in the AppStore and find a few, but that only yields a small handful of candidates.
The only extensions (technically plugins, not extensions) I currently use are mailtrackerblocker which blocks tracking pixels in mail and MailTags. I used to have one that checked DMARC headers, but annoyingly I can’t find it any more.
What else have people found? Is there more out there?