Oh, no, I assume that we speak SMTP when it is agreed upon to do so,
and nothing else
at least systems people should be able to keep separate things
separate, simple and robust.
What you don't take into account is that there are bad actors who do not
follow your agreed upon standards. People will do things you never
intended to find exploits that give them an edge in the world. This has
always been the shortsightedness of the design of the internet. Good
people design things with other good people in mind forgetting there are
bad (and stupid) people in the world.
