There's no private-private e-mail service. There never can be. You think your little tricks, enabled by google to sell you a fake sense of security and convenience are somehow effective - it's just cope for complacency. E-mail has been entirely captured by big providers, Lopp's post about it a few years ago is spot on. Never, ever use e-mail for important, private stuff. Plenty of decent msging solutions are available.

Proton and tuta are most likely honeypots, too.