I'd like to detect and/or enforce that people use encryption when they pass data between systems. For example people say that for SMTP, tcp/25, they use STARTTLS. Is there any way to verify/enforce that STARTTLS is in fact used? I don't want to inspect the content of encrypted traffic, just want to ensure that people encrypt data.
The same question is about STARTTLS for LDAP on tcp/389 or detecting/enforcing the use of HTTPS on non-standard ports.