@hyploma @Tutanota @protonmail @Horizon_Innovations @bthylafh indeed. Most clearnet services are incapable of sending mail to #onion email addresses. Even some onion email services do not accept or send onion mail. And some onion email services can't email clearnet, while others can (but some of those can't put a clearnet reply address in the header).

@bthylafh @Horizon_Innovations @protonmail @Tutanota @hyploma IIRC, elude.in is one of the more versatile ones. It can send email from elude.in to both clearnet & onion recipients, it can receive email via onion or clearnet (you have two address domains), and the UI is accessible by either onion or clearnet. Onionmail may be the same, but most services have on limitation or another.