It would be interesting to start applying filters on email based on recipient MX. i.e. if I see your MX is @yahoo.com, I don't send the mail (or send a mail su

It would be interesting to start applying filters on email based on recipient MX. i.e. if I see your MX is @yahoo.com, I don't send the mail (or send a mail suggesting you move to a better mail provider). Depending on who I am, I may or may not send mail to gmail. If I see it's a self-hosted well configured MX, I probably will send mail and trust in starttls. (You can't just rely on domain extensions due to things like Google Apps for your Domain which lets you customize the domain.)