SPF, which abbreviates Sender Policy Framework, is an authentication system that is aimed at stopping the so-called e-mail counterfeiting. Essentially, it indicates sending a message from one e-mail address and making it seem to be sent from a different one with the purpose to scam in some way the person opening it. If the SPF protection is running for a domain, a record that contains all the mail servers authorized to email messages with addresses within the domain is created. The record is saved on all of the DNS servers that direct the web traffic all over the world, thus they all will identify whether an email message originates from an authentic server or not. The verification is performed at the very first server where the e-mail goes through and in the first case the e-mail message is forwarded, while in the second one it is removed and it never gets to the intended recipient. Using SPF records for your domains will prevent all unauthorized people from making use of your email addresses for malicious purposes.