The war against spam is hard and, to tell you the truth, I'm not sure if the good guys are winning it. Nevertheless there are technologies that really make a difference on the day-to-day battles such as Sender ID.
The Sender ID Framework is an e-mail authentication technology protocol that helps address the problem of spoofing and phishing by verifying the IP address of the sender against the alleged owner of the sending domain. This verification is done by using a special DNS record, the SPF record.
Although there are technical articles describing the configuration process, the easiest way is just to follow the Sender ID Framework SPF Record Wizard.
Other resources:
- Implementation Tips for the Sender ID Framework—Creating Your SPF Record
- The Sender ID Framework: Protecting Your Brand, Users, and Infrastructure
- Sender ID Business Value White Paper