SPF, which abbreviates Sender Policy Framework, is a verification system that is aimed at blocking the so-called email forging. In simple terms, this means sending some message from one email address and making it appear to be sent from a different one with the objective to scam in some way the individual getting it. In the event that the SPF protection is running for a domain name, a record which has all of the mail servers authorized to email messages with addresses within the domain is made. The record is kept on all of the DNS servers that direct the Internet traffic around the world, therefore they all can identify whether an email message originates from a valid server or not. The check is conducted at the first server where the e-mail goes through and in the first case the e-mail message is forwarded, whereas in the second one it's removed and it never gets to the supposed recipient. Employing SPF records for your domains will prevent all unauthorized people from using your email addresses for malicious purposes.