Reminds me of a similar attack on PGP/MIME/HTML where you'd put <a href="http://evil.example/ in front of the PGP message.
Email's in a bad situation with regards to this because every intermediate server is expected to mangle the message and the headers, so the only way to consistently sign something is to make it a marked up encoded block the way PGP does.
Email's in a bad situation with regards to this because every intermediate server is expected to mangle the message and the headers, so the only way to consistently sign something is to make it a marked up encoded block the way PGP does.