SPF, which abbreviates Sender Policy Framework, is a certification system that aims at protecting against the so-called e-mail forging. Essentially, it indicates sending a message from one e-mail and making it seem to be sent from another with the purpose to scam in some way the person opening it. In case the SPF protection is running for a domain name, a record that contains all mail servers authorized to email messages with addresses part of the domain is created. The record is stored on all the DNS servers that route the Internet traffic internationally, therefore they all will identify whether an e-mail message comes from a trustworthy server or not. The check is performed at the first server where the e-mail goes through and in the first case the email message is forwarded, and in the second one it's removed and it never gets to the intended recipient. Employing SPF records for your domain names will prevent any unauthorized people from making use of your email addresses for harmful purposes.