SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that aims at stopping the so-called e-mail forging. Basically, this indicates sending a message from one e-mail and making it seem to be sent from a different one with the purpose to scam in some way the individual getting it. In case the SPF protection is activated for a domain name, a record that includes all of the mail servers authorized to email messages with addresses in the domain is created. The record is placed on all the DNS servers that direct the web traffic worldwide, therefore they all can identify whether an email message comes from a valid server or not. The verification is conducted at the first server where the email goes through and in the first case the e-mail message is forwarded, whereas in the second one it is discarded and it never reaches the intended recipient. Using SPF records for your domains will prevent any unwanted people from using your emails for malicious purposes.