SPF, which abbreviates Sender Policy Framework, is a certification system that aims at blocking the so-called email forging. Basically, this means sending some message from one e-mail address and making it seem to be sent from another with the purpose to scam in some way the person getting it. When the SPF protection is activated for a domain name, a record which includes all the mail servers authorized to email messages with addresses under the domain is created. The record is kept on all the DNS servers that route the web traffic all over the world, so that they all can identify if an e-mail message originates from a legitimate server or not. The check is conducted at the first server where the email goes through and in the first case the message is forwarded, while in the second one it is removed and it never reaches its intended recipient. Employing SPF records for your domains will prevent all unauthorized people from using your email addresses for malicious purposes.