Sure, but the SMTP server won't sign the email if it was sent with the wrong login. So unless I don't trust the whole domain (in which case even PGP could resul

Sure, but the SMTP server won't sign the email if it was sent with the wrong login. So unless I don't trust the whole domain (in which case even PGP could result in a false sense of security), this pretty much verifies the sender. Only thing I need to do is to check if it's correct.