SPF, which is an abbreviation for Sender Policy Framework, is a validation system that aims at stopping the so-called email forging. Basically, it indicates sending some message from one email address and making it look like it’s sent from another with the idea to scam in some way the individual opening it. If the SPF protection is running for a domain name, a record which includes all the mail servers authorized to send messages with addresses under the domain is created. The record is placed on all the DNS servers that direct the Internet traffic internationally, therefore they all can recognize if an e-mail message originates from a valid server or not. The check is performed 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 removed and it never gets to the supposed recipient. Using SPF records for your domains will stop any unauthorized people from using your emails for malicious objectives.