The surface of HTML+CSS is pretty big by now. Perhaps you could use CSS to restyle the "From" address: hide the original content and use an :after property to put "$bank_name" there. Perhaps you can generate a unique @font url for each user to track opening of messages. Just two things of the top of my head that maybe won't work, but it would probably be a cat and mouse game for a while when security researchers start poking at it.