Proton Mail encrypts your mail at rest, and they do not store the decryption keys, so theoretically Proton Mail cannot read your normal emails unless they inter

Proton Mail encrypts your mail at rest, and they do not store the decryption keys, so theoretically Proton Mail cannot read your normal emails unless they intercept and store them during sending or receiving. This is already a benefit whether your contacts use encrypted email or not. There is a way to send an encrypted message to any other email address, but you have to share a password with them somehow, either by including a hint or by some other channel. It is essentially encrypting and storing the message on Proton Mail servers, and then giving the recipient a link to un-encrypt it (they must know the password to do this). I'm not sure if this process is zero-knowledge or not. In addition all Proton Mail to Proton Mail emails are end-to-end encrypted. These are not as good as if everybody used email encryption, and it was all end-to-end zero-knowledge, but it's better than the status-quo, in my opinion at least.