It's a pity that anonymous remailers aren't more widely used, but I've been thinking of an 80/20 solution that might be easier to adopt. Imagine that alice@pro

It's a pity that anonymous remailers aren't more widely used, but I've been thinking of an 80/20 solution that might be easier to adopt. Imagine that alice@protonmail wants to send an encrypted message to bob@tutanota and they both have each other's PGP keys. What these email providers could do is offer a reserved email address (such as remailer@) with its own associated PGP public key. (The address and the public key could be stored in the DNS, or retrieved via some HTTPS .well-known URL). This way alice@protonmail could encrypt a message (including headers) to bob@tutanota using his private key, and then encrypt this inner message as the body of a message sent to remailer@tutanota. ProtonMail would only see that Alice is communicating with a Tutanota user, and Tutanota would only see that Bob is communicating with a ProtonMail user. (For the specific case of webmail providers, you would also want something like SXG [1] combined with Binary Transparency [2] to prevent malicious JavaScript being served). [1] https://developers.google.com/web/updates/2018/11/signed-exchanges https://developers.google.com/web/updates/2018/11/signed-exc... [2] https://wiki.mozilla.org/Security/Binary_Transparency https://wiki.mozilla.org/Security/Binary_Transparency