@h3artbl33d @ajdonovan2k I've only heard of ProtonMail out of the set you mentioned. As for why I didn't choose them; it's my understanding that ProtonMail's safeguards are only effective when sending mail to other ProtonMail users.

I have a ProtonMail account, but I save it for when I need a secure channel or for when somebody requests a more secure venue. Most of the time I don't, and if I suddenly went completely dark it would probably raise flags.