SPF, which abbreviates Sender Policy Framework, is an authentication system that is aimed at protecting against the so-called email counterfeiting. Essentially, it indicates sending some message from one e-mail and making it appear to be sent from a different one with the idea to scam in some manner the person getting it. In the event that the SPF protection is active for a domain, a record that includes all mail servers authorized to send messages with addresses under the domain is made. The record is stored on all of the DNS servers that direct the Internet traffic worldwide, thus they all can recognize whether an e-mail message comes from a valid server or not. The verification is performed at the first server where the email goes through and in the first case the message is forwarded, but in the second it is discarded and it never gets to its intended recipient. Using SPF records for your domain names will stop all unauthorized people from using your emails for harmful objectives.