So now to send email over SMTP it is required to host policy on.. HTTPS server? (or else all your mail will end up in spam?) Why it isn't just extra TXT DNS rec

So now to send email over SMTP it is required to host policy on.. HTTPS server? (or else all your mail will end up in spam?) Why it isn't just extra TXT DNS record indicating that TLS is required? EDIT: I think DANE TLSA records are already doing that.