SPF, which abbreviates Sender Policy Framework, is a certification system that aims at protecting against the so-called e-mail counterfeiting. In simple terms, this means sending some message from one email address and making it seem to be sent from a different one with the purpose to scam in some way the individual opening it. When the SPF protection is running for a domain, a record that contains all mail servers authorized to send messages with addresses within the domain is made. The record is saved on all DNS servers that route the web traffic across the globe, so they all will identify if an email message originates from a trustworthy server or not. The check is done at the first server where the email goes through and in the first case the message is forwarded, and in the second one it is removed and it never gets to its intended recipient. Applying SPF records for your domain names will prevent any unwanted people from using your email addresses for harmful purposes.