We wrote pretty much this years ago at FastMail: https://www.fastmail.fm/help/technical/ssltlsstarttls.html https://www.fastmail.fm/help/technical/ssltlsstartt

We wrote pretty much this years ago at FastMail: https://www.fastmail.fm/help/technical/ssltlsstarttls.html https://www.fastmail.fm/help/technical/ssltlsstarttls.html All the downgrade and pre-encryption MITM and complexity arguments are definitely worth repeating though. Straight up SSL is significantly better.