SPF, which is an abbreviation for Sender Policy Framework, is a validation system that is aimed at stopping the so-called e-mail faking. Essentially, this means sending some message from one e-mail address and making it look like it’s sent from a different one with the purpose to scam in some way the person getting it. In the event that the SPF protection is running for a domain name, a record which has all the mail servers authorized to send messages with addresses within the domain is created. The record is stored on all the DNS servers that direct the web traffic worldwide, so that they all will recognize if an email message originates from a legitimate server or not. The check is done at the very first server where the e-mail goes through and in the first case the email message is forwarded, whereas in the second one it's discarded and it never reaches the supposed recipient. Employing SPF records for your domains will stop any unwanted people from making use of your emails for malicious purposes.