There is someone from whom I no longer wish to receive emails. The obvious solution is to blacklist them.
Or...if you're using Apple Mail, you can go to Preferences/Rules and set up a rule that deletes offending email before it ever reaches your machine. It's a function I've used successfully for junk mail.
I found that some junk mail would have an "Unsubscribe" process (even though I hadn't "subscribed" in the first place) but the "Unsubscribe" was simply a fishing expedition to extract information. i.e. the site wanted information it could not already have.