SPF, which is an abbreviation for Sender Policy Framework, is a certification system that is aimed at stopping the so-called email counterfeiting. Basically, this means sending a message from one email and making it seem to be sent from another with the idea to scam in some way the person getting it. In the event that 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 generated. The record is kept on all the DNS servers that route the web traffic around the world, so that they all will identify whether an e-mail message originates from a trustworthy server or not. The check is done at the first server where the e-mail goes through and in the first case the email message is forwarded, but in the second one it is discarded and it never reaches the intended recipient. Using SPF records for your domain names will prevent all unauthorized people from making use of your email addresses for harmful objectives.