SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that aims at preventing the so-called email faking. In simple terms, it indicates sending a message from one e-mail and making it look like it’s sent from a different one with the objective to scam in some way the individual receiving it. When the SPF protection is active for a domain, a record that contains all the mail servers authorized to email messages with addresses in the domain is made. The record is saved on all DNS servers that route the Internet traffic around the world, therefore they all can recognize if an e-mail message comes from a legitimate server or not. The check is conducted at the first server where the email goes through and in the first case the email message is forwarded, whereas in the second one it's discarded and it never gets to the supposed recipient. Using SPF records for your domains will stop any unwanted people from making use of your email addresses for malicious objectives.