SPF, which is an abbreviation for Sender Policy Framework, is a verification system that is aimed at protecting against the so-called email faking. In simple terms, it indicates sending a message from one e-mail address and making it look like it’s sent from another one with the objective to scam in some way the individual getting it. When 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 generated. The record is kept on all of the DNS servers that route the web traffic globally, so they all can recognize if an e-mail message comes from an authentic 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, but in the second it's removed and it never gets to its intended recipient. Employing SPF records for your domain names will stop all unwanted people from using your email addresses for malicious purposes.