Currently, Postfix is set up to send encrypted email using TLS, but not all destinations support TLS encryption.
I assume it's possible to configure Postfix so that it securely relays the mail to another server ONLY upon TLS authentication failure to the original destination. That way, if mail can't be sent and received directly by the intended party, then there's an alternate method or routing the mail so that ultimate the intended recipient can to access it, like through a portal, for example.