I'm not familiar with those services, do they not provide POP3, SMTP, IMAP addresses? I've been using my own email setup for ~15 years, but have recently considered looking into some of these online services. I'd require the ability to use a local client to connect, however. Now you have me a little concerned.
I use ProtonMail + Thunderbird, it does require a client to handle the decryption/encryption to the servers. It was open sourced a while ago which is nice, although admittedly it'd be nice to have it just work.
That's cool, I wasn't aware Protonmail had this feature. I use Tutanota and their client is required to access their service, which does work great as is.
They are specialised in providing encrypted storage of email, as well as end to end encrypted emails between their users. These features requires some measures which deviate from the plaintext standard protocols.
