Rizzler Tbh since its not end to end encrypted unless both ends are using proton, I don't see the selling point of this specifically.
Almost half of everyone I ever mail are also using Proton, but yeah, we really need a standard for end-to-end encryption in email that federates between providers properly. But maybe everyone thinks email is legacy at this point for anything else than account sign-ups.
Rizzler I've started to take a liking to cock.li since they are honest about what they can/can't do
Proton is also encrypting all non-encrypted email received for your inbox, so only you can decrypt it. A very big reason for doing this is to protect themselves from law enforcement requests for data. By not having the data, they avoid being overloaded with such requests that they have to comply with, and avoid the bad publicity linked to having to hand over user data. Well mostly at least, sometimes law enforcement has been happy enough with obtaining IP logs. There used to be a very reputable email provider Lavabit, that was similar to the one you link, except no vulgar or excluding language, and always free. They were honest that emails weren't encrypted. But then suddenly US law enforcement demands them to hand out all mails belonging to an "esnowden" having an account there. Lavabit shut down their service after that, as you can probably imagine. They said they cannot protect users such as whistleblowers. Yeah, Edward Snowden revealed he was the one leaking NSA documents shortly after that. This whole event was what caused Tutanota and ProtonMail to be formed. They realized all mails need to be encrypted for the user inbox such that they cannot hand over emails on demand. And of course both of them added end-to-end encryption for mails sent between users of each provider. The reason Facebook are now introducing end-to-end encryption in Messenger is not because Facebook care about user privacy, they don't, at all. They do it to protect themselves from law enforcement. The less data they can hand over, the less of a target they will be. And now after Telegram, one of the few chat apps that was still entirely unencrypted where forced to hand over massive amounts of user data, Discord quickly decided to also start switching over to end-to-end encryption, even if they have been opposing it in the past. To protect themselves from that.
I am afraid the email provider you link aren't very secure at all. They are honest about it, but there are reasons Tutanota and ProtonMail were made.