SPF, which abbreviates Sender Policy Framework, is a certification system that aims at protecting against the so-called email forging. Basically, this means sending a message from one email and making it seem to be sent from another with the purpose to scam in some manner the person getting it. If the SPF protection is active for a domain, a record that includes all of the mail servers authorized to email messages with addresses within the domain is generated. The record is placed on all the DNS servers that direct the web traffic worldwide, so that they all will recognize if an e-mail message comes 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, but in the second it is removed and it never reaches the intended recipient. Using SPF records for your domains will prevent any unwanted people from making use of your emails for harmful objectives.