Okay, you configure Postfix to verify TLS. Validation fails, what will happen? What does the documentation say about that configuration option? That aside, an

Okay, you configure Postfix to verify TLS. Validation fails, what will happen? What does the documentation say about that configuration option? That aside, an active attacker can also trivially force a downgrade. Only with the introduction of MTA-STS, connections between MTA-MTA are secure. That's supported by, like, few major players - I guess by volume a fine percentage, but by total count, abysmal.