SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that aims at protecting against the so-called e-mail counterfeiting. In simple terms, this indicates sending a message from one email and making it look like it’s sent from a different one with the objective to scam in some manner the individual opening it. If the SPF protection is running for a domain name, a record which contains all mail servers authorized to send messages with addresses within the domain is created. The record is kept on all the DNS servers that direct the Internet traffic globally, so they all can identify whether an e-mail message originates from a valid server or not. The check is conducted at the first server where the e-mail goes through and in the first case the message is forwarded, whereas in the second one it's discarded and it never gets to the supposed recipient. Applying SPF records for your domains will prevent any unauthorized people from using your email addresses for harmful objectives.