SPF, which abbreviates Sender Policy Framework, is a validation system that aims at blocking the so-called email faking. In simple terms, this indicates sending a message from one e-mail address and making it seem to be sent from another with the purpose to scam in some manner the individual opening it. When the SPF protection is active for a domain name, a record that contains all the mail servers authorized to send messages with addresses part of the domain is generated. The record is stored on all DNS servers that route the web traffic internationally, so they all can recognize if an email message originates from a legitimate server or not. The check is performed at the very first server where the email goes through and in the first case the e-mail message is forwarded, whereas in the second one it's removed and it never reaches the supposed recipient. Using SPF records for your domains will prevent all unwanted people from making use of your email addresses for malicious purposes.