[LeoPanthera]

ProtonMail is an interesting case. It does not provide SMTP or IMAP servers, except via a weird proxy service that runs on your local machine, and obviously isn't compatible with smartphones.

It may still class as an "email service", but only just, since it is effectively limited to webmail and their custom apps.

[flkiwi]

I have a protonmail app on my iPhone. Works great.

[nix23]

>ProtonMail is an interesting case. It does not provide SMTP or IMAP servers,

Just half-true..

https://proton.me/support/imap-smtp-and-pop3-setup

[LeoPanthera]

...that says exactly what I said in my comment. I'm not sure why I deserve a "half true".