Hello, thank you for the question. ProtonMail is a different kind of email for a different kind of audience, so it depends on what your needs are. Honestly, we're ourselves puzzled over benefits of ProtonMail over just using yourself GPG.

This is such a bizarre question. Protonmail is not a standards based mail service. No IMAP, no SMTP. It's client-side encrypted and only works via webmail or their own mobile app.