SPF, which is an abbreviation for Sender Policy Framework, is a validation system that aims at stopping the so-called e-mail forging. Essentially, it indicates sending a message from one e-mail address and making it appear to be sent from another with the idea to scam in some way the person opening it. In the event that the SPF protection is running for a domain name, a record that contains all the mail servers authorized to email messages with addresses part of the domain is generated. The record is kept on all of the DNS servers that route the Internet traffic all over the world, therefore they all can recognize if an e-mail message comes from a valid server or not. The check is performed at the first server where the email goes through and in the first case the e-mail message is forwarded, but in the second it is discarded and it never reaches the intended recipient. Applying SPF records for your domain names will prevent any unauthorized people from making use of your email addresses for harmful purposes.