Sender Authentication: What Is It, and How Can It Help You?

IF: Could you define Sender Policy Framework (SPF)?
Guerra: This system was originally authored in a grass-roots movement that was adopted by and championed by America Online. SPF is an e-mail protocol that allows recipient systems to verify that the sending server name listed in the message header agrees with the Internet Protocol (IP) address that sent the message. Faking the server name is very easy, but faking the IP address is extraordinarly difficult. SPF validates information that is visible to the ISP but is rarely visible to the person who will ultimately read the message.