SPF, which is an abbreviation for Sender Policy Framework, is a certification system that aims at blocking the so-called e-mail counterfeiting. In simple terms, this indicates sending some message from one e-mail and making it appear to be sent from another one with the purpose to scam in some way the individual receiving it. When the SPF protection is activated for a domain name, a record which has all of the mail servers authorized to send messages with addresses part of the domain is created. The record is placed on all DNS servers that route the Internet traffic worldwide, so that they all can identify if an e-mail message originates from a valid server or not. The check is done at the first server where the email goes through and in the first case the email message is forwarded, while in the second it's discarded and it never gets to the intended recipient. Applying SPF records for your domains will prevent all unauthorized people from making use of your emails for harmful objectives.