SPF, which abbreviates Sender Policy Framework, is a verification system that aims at blocking the so-called email forging. In simple terms, this means sending a message from one email and making it appear to be sent from a different one with the idea to scam in some way the individual getting it. In the event that the SPF protection is running for a domain, a record which includes all the mail servers authorized to send messages with addresses part of the domain is made. The record is saved on all DNS servers that direct the Internet traffic internationally, therefore they all can recognize if an e-mail message originates from a legitimate server or not. The check is done at the very first server where the e-mail goes through and in the first case the email message is forwarded, but in the second it is removed and it never reaches its intended recipient. Using SPF records for your domain names will prevent all unauthorized people from using your emails for malicious purposes.