SMTP Strict Transport Security

I don't get it. If anything, a secured connection is client policy. If the server claims not to support it, then you have two scenarios:

1. You're an opportunistic user - you do choose to fall back to unsecured SMTP, but you don't really need a secure connection anyway

2. You mandate a secure connection - you don't fall back and do not use the service

A man in the middle can deny service, but we already knew that.