SPF, which abbreviates Sender Policy Framework, is a certification system that is aimed at protecting against the so-called email forging. Essentially, it indicates sending some message from one email address and making it seem to be sent from another with the purpose to scam in some manner the individual getting it. In the event that the SPF protection is active for a domain name, a record which contains all of the mail servers authorized to email messages with addresses within the domain is generated. The record is saved on all DNS servers that direct the web traffic around the world, thus they all will recognize whether an e-mail message comes from a trustworthy 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 its intended recipient. Employing SPF records for your domains will stop all unauthorized people from making use of your emails for malicious purposes.