That can be done with Thunderbird/Enigmail and with GPGTool in mail.app. If the key is on a public server, then decryption can be done by anyone. The point is

That can be done with Thunderbird/Enigmail and with GPGTool in mail.app. If the key is on a public server, then decryption can be done by anyone. The point is that Proton is categorically not E2EE sending to 3rd parties. It can’t be because email doesn’t work like that. PGP is a bandaid. If you want to send email securely, don’t use email!