SPF, which abbreviates Sender Policy Framework, is an authentication system that aims at protecting against the so-called e-mail counterfeiting. Essentially, this means sending a message from one e-mail address and making it seem to be sent from another one with the purpose to scam in some manner the person getting it. In the event that the SPF protection is active 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 kept on all the DNS servers that direct the Internet traffic worldwide, so that they all will identify whether an email message originates from a valid server or not. The check is done at the first server where the e-mail goes through and in the first case the message is forwarded, whereas in the second it's discarded and it never gets to its intended recipient. Employing SPF records for your domains will stop all unauthorized people from making use of your emails for harmful purposes.