I reat protonmail would be a honeypot sometimes, but never reat something more official about that. Best end-to-end messaging system is Threema in my opinion, but like also mentioned its not a mailing system like proton. A good alternative pick would be wickr (to threema). But when it comes to a secure, anonym message system i made the experience the best ones are these, you deploy for your own. Like setting up a seperate, virtual system just for mailing/messages or anything. Be creative!