SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that aims at blocking the so-called e-mail counterfeiting. Basically, this means sending some message from one e-mail and making it seem to be sent from another with the idea to scam in some manner the individual getting it. If the SPF protection is active for a domain name, a record which has all of the mail servers authorized to send messages with addresses part of the domain is created. The record is placed on all DNS servers that route the web traffic across the globe, so that they all can recognize whether an email message comes from an authentic server or not. The verification is conducted at the very first server where the email goes through and in the first case the email message is forwarded, but in the second one it's discarded and it never gets to the supposed recipient. Employing SPF records for your domains will stop any unwanted people from making use of your email addresses for harmful purposes.