SPF, which is an abbreviation for Sender Policy Framework, is a verification system that is aimed at protecting against the so-called e-mail faking. In simple terms, this means sending some message from one e-mail and making it seem to be sent from another one with the objective to scam in some way the individual opening it. In case the SPF protection is running for a domain name, a record that contains all of the mail servers authorized to send messages with addresses in the domain is created. The record is stored on all DNS servers that route the web traffic all over the world, therefore they all can identify whether an e-mail message originates from a trustworthy server or not. The verification is performed at the very first server where the email goes through and in the first case the email message is forwarded, and in the second it's removed and it never reaches the supposed recipient. Applying SPF records for your domains will stop all unwanted people from using your email addresses for malicious objectives.