You might want ProtonMail or Tutanota if you wish, but having it accessible over my Mobile app of choice was a blocker for me.
Some of the extra credits that made me choose Migadu:
* Their site works without JavaScript enabled
* Very simple and lightweight
* Strong support for standards and portability
* Open Source (as in FOSS) Stack, including their UI. https://git.sr.ht/~migadu/
* They're not after investors or scaling: https://www.migadu.com/procon/