SPF, which is an abbreviation for Sender Policy Framework, is a validation system that aims at preventing the so-called email counterfeiting. Basically, this means sending a message from one email and making it look like it’s sent from another one with the purpose to scam in some way the person opening it. In the event that the SPF protection is activated for a domain, a record that includes all mail servers authorized to email messages with addresses under the domain is created. The record is placed on all DNS servers that route the Internet traffic globally, therefore they all can recognize whether an email message comes from a legitimate server or not. The verification 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's removed and it never reaches the supposed recipient. Using SPF records for your domain names will prevent any unauthorized people from making use of your emails for harmful objectives.