The Sender Policy Framework seems to be the solution we have all waited for for a long time. By simply adding a single DNS record (type TXT) to your domains, you can announce which computers are allowed to deliver e-mail from your domains. So it is checked by the receiving SMTP server before even accepting the content (also significantly reducing bandwith usage). While this is probably not the end to Spam in total, it might be the end to Spam as we know it today: coming in masses, forging your e-mail addresses, difficult to trace back, severely annoying.
The SPF guys have some excellent documentation material on their web site. There are some insightful slide shows as well: a detailed introduction teaching you the different scenarios, a detailed explanation of the anatomy of a SPF DNS record, a hacker‘s intro to What is spam? (“spammers feared to develop weapons of mass destruction!!!) and more. In addition, you find a setup wizard makes setting up the DNS TXT record easy. The SPF Adoption Roll tracks popular domains for their SPF support. So far a bit more than 10000 domains world-wide have adopted SPF – but among them you find important major mail providers like AOL, Hotmail and others.
To round up the good documentation there is the SPF Wiki. Let‘s all support SPF today! It can make a difference.