SPF, which abbreviates Sender Policy Framework, is a verification system that is aimed at protecting against the so-called e-mail faking. In simple terms, it indicates sending a message from one e-mail address and making it seem to be sent from another one with the purpose to scam in some manner the person receiving it. In case the SPF protection is running for a domain name, a record that includes all the mail servers authorized to email messages with addresses in the domain is created. The record is saved on all the DNS servers that direct the Internet traffic around the world, so that they all will recognize whether an email message comes from a valid server or not. The check 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 is removed and it never reaches the supposed recipient. Using SPF records for your domains will prevent any unwanted people from using your email addresses for harmful purposes.