SPF, which abbreviates Sender Policy Framework, is a verification system that is aimed at preventing the so-called e-mail forging. Basically, this means sending some message from one e-mail and making it seem to be sent from another one with the purpose to scam in some manner the individual opening it. If the SPF protection is running for a domain name, a record which contains all the mail servers authorized to send messages with addresses under the domain is created. The record is saved on all DNS servers that direct the web traffic worldwide, so that they all can identify whether an email message comes from a valid server or not. The check is conducted at the very first server where the e-mail goes through and in the first case the message is forwarded, but in the second it's removed and it never reaches the intended recipient. Applying SPF records for your domain names will prevent any unwanted people from using your email addresses for harmful objectives.