I figured it was obvious, given 1.5B people use GMail so it's probably the largest receiver of email in the world. So even if "email is open" if there's a closed system on the receiving end of your message it doesn't do you much good.
Maybe it's not obvious though, and we're just talking theoretical techno-utopias.
Maybe it's not obvious though, and we're just talking theoretical techno-utopias.