SPF, which abbreviates Sender Policy Framework, is a verification system that aims at stopping the so-called e-mail faking. Basically, it indicates sending a message from one email and making it look like it’s sent from a different one with the purpose to scam in some way the individual receiving it. In case the SPF protection is running for a domain name, a record which includes all of the mail servers authorized to send messages with addresses within the domain is made. The record is placed on all the DNS servers that direct the Internet traffic worldwide, thus they all will identify if an email message originates from a trustworthy server or not. The check is conducted at the very 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 unwanted people from making use of your email addresses for harmful purposes.