SPF, which abbreviates Sender Policy Framework, is a validation system that is aimed at protecting against the so-called e-mail counterfeiting. In simple terms, this means sending some message from one email address and making it look like it’s sent from another one with the purpose to scam in some way the person receiving it. In the event that the SPF protection is active for a domain name, a record which includes all of the mail servers authorized to email messages with addresses part of the domain is generated. The record is kept on all DNS servers that direct the Internet traffic worldwide, so they all will identify if an email message originates from an authentic server or not. The verification is conducted at the first server where the e-mail goes through and in the first case the e-mail message is forwarded, whereas in the second it's discarded and it never reaches the intended recipient. Using SPF records for your domain names will prevent all unauthorized people from using your emails for harmful purposes.