SPF, which abbreviates Sender Policy Framework, is a verification system that is aimed at blocking the so-called e-mail forging. Basically, it indicates sending some message from one email address and making it seem to be sent from another one with the purpose to scam in some way the individual receiving it. When the SPF protection is active for a domain, a record that contains all mail servers authorized to send messages with addresses part of the domain is made. The record is kept on all the DNS servers that direct the Internet traffic worldwide, so that they all will identify whether an e-mail message comes from a legitimate server or not. The check is conducted at the first server where the e-mail goes through and in the first case the message is forwarded, while in the second one it is removed and it never reaches the intended recipient. Applying SPF records for your domain names will stop any unauthorized people from making use of your email addresses for harmful purposes.