One of the biggest security gaps in SMTP is that failing to establish TLS will result in falling back to plaintext; it's opportunistic TLS. Senders and receiver

One of the biggest security gaps in SMTP is that failing to establish TLS will result in falling back to plaintext; it's opportunistic TLS. Senders and receivers don't perform path validation because a validation failure will not stop a message from being sent -- it will just be sent with plaintext. The missing piece is widespread support for a way for receiving mail servers to declare that they support TLS (and optionally identify their CA or pin their certificate), such that it will instruct senders to connect with mandatory TLS instead of opportunistic TLS. With a protocol like this in place, senders can begin performing path validation of the receiver's certificate when they connect, but only for receivers who declare it, allowing an incremental nonbreaking rollout. Once widespread support is in place, we can begin making an effort to require validated certificates. By the way, you might be interested in Google's email transparency report, where they publish statistics on TLS adoption: http://www.google.com/transparencyreport/saferemail/ http://www.google.com/transparencyreport/saferemail/ I'd be interested to chat with anyone about email security and ideas to improve it; feel free to reach out. I would gladly put my support behind and implement a proposal that will solve these problems.