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 d

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. [1]: https://proton.me/support/proton-mail-encryption-explained https://proton.me/support/proton-mail-encryption-explained