SPF, which is an abbreviation for Sender Policy Framework, is an authentication system that is aimed at preventing the so-called e-mail counterfeiting. In simple terms, this indicates sending some message from one e-mail address and making it look like it’s sent from another with the objective to scam in some way the person getting it. If the SPF protection is active for a domain, a record which has all the mail servers authorized to email messages with addresses under the domain is created. The record is placed on all DNS servers that route the web traffic across the globe, so that they all will identify whether an e-mail message comes from a legitimate server or not. The verification is performed at the first server where the email goes through and in the first case the email message is forwarded, while in the second one it's discarded and it never gets to the supposed recipient. Using SPF records for your domain names will prevent all unauthorized people from making use of your email addresses for malicious objectives.