SPF, which is an abbreviation for Sender Policy Framework, is a verification system that is aimed at blocking the so-called e-mail faking. In simple terms, it indicates sending some message from one e-mail and making it seem to be sent from a different one with the objective to scam in some manner the individual getting it. In the event that the SPF protection is running for a domain, a record that includes all of the mail servers authorized to email messages with addresses under the domain is made. The record is kept on all the DNS servers that route the Internet traffic internationally, thus they all can recognize whether an e-mail message comes from a legitimate server or not. The check is performed at the first server where the e-mail goes through and in the first case the email message is forwarded, but in the second one it's discarded and it never reaches the supposed recipient. Employing SPF records for your domains will prevent any unwanted people from using your emails for harmful purposes.