That doesn't stop you getting all the bounced and angry e-mails tho! Mail clients (and users!) are not that clever. The only way to resolve this is to form an entirely new way of sending e-mail, and as someone has already pointed out - that is just not going to happen - at least not in the foreseeable future anyway.
That sounds about right - I once opened up our mail server (when I was in IT) for a customer who wanted to send a few e-mails through our server - very soon after I found our mail server running slowly and discovered it delivering thousands of messages. It wasn't more than a couple of hours after I had opened it up (as a temporary measure I may add!) and this must have been at least 6 years ago now, so I can only imagine that spammers find open mail servers even quicker now. Anyone who has sat and watched a firewall blocking attempts to gain entry to a machine connected directly to the Internet will know just how many attempts there are to probe that machine to find its weaknesses.
Matt