SPF, which abbreviates Sender Policy Framework, is a verification system that aims at stopping the so-called email counterfeiting. Essentially, this indicates sending some message from one e-mail address and making it look like it’s sent from another with the purpose to scam in some manner the person getting it. In case the SPF protection is active for a domain, a record that includes all of the mail servers authorized to email messages with addresses part of the domain is made. The record is stored on all of the DNS servers that route the web traffic across the globe, so that they all can recognize if an email message comes from a valid server or not. The check is done at the very first server where the email goes through and in the first case the message is forwarded, and in the second one it's removed and it never gets to the supposed recipient. Applying SPF records for your domains will prevent all unauthorized people from using your emails for harmful objectives.