Sender Policy Framework (SPF) – Anti-Forgery Solution
http://www.openspf.org//

SPF fights return-path address forgery and makes it easier to identify spoofs. Domain owners identify sending mail servers in DNS. SMTP receivers verify the envelope sender address against this information, and can distinguish authentic messages from forgeries before any message data is transmitted. This has been added to World Wide Web Reference Subject Tracer™ Information Blog.