SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that is aimed at preventing the so-called e-mail counterfeiting. In simple terms, this means sending some message from one e-mail address and making it appear to be sent from another with the purpose to scam in some manner the individual receiving it. In case the SPF protection is active for a domain, a record which contains all mail servers authorized to send messages with addresses under the domain is created. The record is placed on all the DNS servers that route the web traffic worldwide, therefore they all can recognize if an e-mail message comes from a legitimate server or not. The verification is performed at the very first server where the email goes through and in the first case the email message is forwarded, but in the second it is discarded and it never gets to its intended recipient. Applying SPF records for your domains will stop all unwanted people from using your emails for harmful objectives.