Forging of origin address

Ok, here is an attempt to try to follow Dave's suggestion and
word something in terms of user requirements:

I would like to have a system where nobody can create/send mail that
purports to come from me/my address but doesn't. Myself getting mail
that purports to be from me is one of the weirdest and most frightening
things that I have seen. And imagining others getting such mail
doesn't make things any better.

And this should of course be possible very easily, without me or the
recipient having to do anything special for each mail.

Sorry for being so egocentric, but of course by extension, I would
like to have a system where email from other people/addresses cannot
be faked. Getting mail purportedly from people you know but that
isn't from them is only slightly less frightening and weird than
getting yourself faked.

Regards,   Martin.