SPF, which abbreviates Sender Policy Framework, is a validation system that aims at stopping the so-called e-mail faking. Basically, this means sending a message from one email and making it seem to be sent from a different one with the purpose to scam in some manner the individual getting it. If the SPF protection is activated for a domain, a record that contains all of the mail servers authorized to send messages with addresses under the domain is generated. The record is placed on all DNS servers that route the Internet traffic worldwide, so that they all can recognize if an e-mail message comes from a trustworthy server or not. The check is performed at the very first server where the e-mail goes through and in the first case the message is forwarded, but in the second it's discarded and it never gets to the supposed recipient. Applying SPF records for your domains will prevent any unwanted people from using your emails for malicious objectives.