I'm a paying customer (paid for 2 years upfront), and I only found out after paying that ProtonMail has an incredibly poor implementation of 2FA. All it supports is app-based authentication[1].
No support for U2F (FIDO) keys[2].
No support for sending SMS to phones.
In comparison, my Google account is protected with: (a) three distinct U2F FIDO keys that are stored safely in different countries, (b) three separate phones for SMS authentication (my phone, dad's pone, mom's phone), (c) lastly there's the authenticator app which I rarely use. This is so much more versatile and reassuring that ProtonMail's extremely-mininal 2FA implementation.
Also, ProtonMail has no excuse for not supporting SMS-based 2FA. They can send a SMS to your phone, when you setup a new account -- but for some reason can't do this for 2FA. Despite being a paid service, they trying to save on the SMS charges that SMS-based 2FA would incur?
Not sure about the other stuff, but SMS 2FA is generally frowned upon for auth.. though obviously they've decided it's fine for the one time setup just as a verification on signup (not used as 2fa in that case, more like crude proof of identity). U2F has been a challenge for everyone from what I've seen.
No support for U2F (FIDO) keys[2].
No support for sending SMS to phones.
In comparison, my Google account is protected with: (a) three distinct U2F FIDO keys that are stored safely in different countries, (b) three separate phones for SMS authentication (my phone, dad's pone, mom's phone), (c) lastly there's the authenticator app which I rarely use. This is so much more versatile and reassuring that ProtonMail's extremely-mininal 2FA implementation.
Also, ProtonMail has no excuse for not supporting SMS-based 2FA. They can send a SMS to your phone, when you setup a new account -- but for some reason can't do this for 2FA. Despite being a paid service, they trying to save on the SMS charges that SMS-based 2FA would incur?
[1] https://protonmail.com/support/knowledge-base/two-factor-aut...
[2] https://en.wikipedia.org/wiki/Universal_2nd_Factor