Hi,
Spam is not hard to locate and track and do something about it, if folks are attentive to it. The problem is that when you have someone waiting for it, it never arrives! But the real issue should be that most mail servers should kill spoof'ing on the spot and they don't, because about one third to one half of your email would be dead.
It was originally thought that IPv6 would help because the mail servers would have to have a specific identifier, but that was killed and most big names did not take advantage of that process, including Microsoft, and many others, because they themselves use the process underneath without you knowing to get themselves information, and this same style is used by other folks to think that they got a "hit", upon which the cost and efficiency of Yahoo and Google is depending ... and until some of that gets addressed, that is the money versus abuse side of it, this crap will continue.
This is a simplified view of it ... by no means is this literal.