But you can’t debundle those — you cannot get ProtonMail (which doesn’t have IMAP) without ProtonCalendar (which doesn’t have CalDAV), ProtonVPN, Proton Password Manager, and an expanding suite of services I already have solutions for that I like better. Being cheaper and only doing mail is a huge plus.
they offer a web client, so, they already have decryption keys for your email. They should just offer IMAPS like everybody else and stop pretending they couldn’t read your email if they wanted to.
They say[1] they only store subject line and to/from addresses accessible to them.
This should be sufficient to implement a web client which does client-side decryption of the content, in which case they indeed could not read the contents.
And they do have the IMAP bridge, I've been using it for a year with Thunderbird without any issues so far.