SPF, which abbreviates Sender Policy Framework, is an authentication system that aims at protecting against the so-called email counterfeiting. In simple terms, this means sending some message from one email address and making it seem to be sent from another one with the objective to scam in some manner the person getting it. When the SPF protection is running for a domain, a record that contains all of the mail servers authorized to send messages with addresses under the domain is made. The record is saved on all DNS servers that route the web traffic internationally, therefore they all will recognize if an email message comes from a valid 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, and in the second it's removed and it never reaches the intended recipient. Using SPF records for your domain names will stop any unauthorized people from making use of your emails for harmful objectives.