> Now there's PGP, but that would look conspicuous. Also, it doesn't hide the authenticated user, envelope mail from or envelope rcpt to values used in the mes

> Now there's PGP, but that would look conspicuous. Also, it doesn't hide the authenticated user, envelope mail from or envelope rcpt to values used in the message, unless, like you said, the sender and recipient(s) are using their own SMTP servers.