In that case one could create an extension that creates a PGP keypair _for the recipient_, attaches encrypted crap to the e-mail, and deletes the private key. I

In that case one could create an extension that creates a PGP keypair _for the recipient_, attaches encrypted crap to the e-mail, and deletes the private key. Is that what you mean? The idea is to add by default an encrypted message to all e-mails that contain nothing useful, to make it indistinguishable from e-mails that do contain useful encrypted stuff. Is that possible? Does it make any sense?