I use (and created) Port87. Its goal is to reduce spam, but the way it works has a byproduct of being inherently rather private. You give out a different address to each place.

It is not end-to-end encrypted, so if that’s a deal breaker for you, I’m afraid it won’t work. That might be in the extended roadmap, but there are a lot of other features I need to build first (IMAP, CardDAV, mailing lists, and a better composition experience are my top priorities right now).