SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that is aimed at blocking the so-called email faking. In simple terms, it indicates sending some message from one e-mail address and making it seem to be sent from another one with the purpose to scam in some way the person receiving it. In case the SPF protection is running for a domain, a record that contains all of the mail servers authorized to email messages with addresses under the domain is created. The record is placed on all the DNS servers that direct the web traffic worldwide, therefore they all will recognize if an email message originates from a legitimate server or not. The check is done at the first server where the email goes through and in the first case the email message is forwarded, and in the second one it's removed and it never gets to its intended recipient. Employing SPF records for your domain names will prevent all unwanted people from using your email addresses for malicious objectives.