SPF, which means Sender Policy Framework, is an e-mail security system, that is designed to validate whether an email message is sent by a certified server. Using SPF protection for a given domain will stop the counterfeiting of emails generated with the domain. In layman's terms: enabling this feature for a domain name generates a particular record in the Domain Name System (DNS) which includes the IP addresses of the servers that are allowed to send emails from mail boxes using the domain. When this record propagates worldwide, it will exist on all of the DNS servers that direct the Internet traffic. Every time a new e-mail message is sent, the first DNS server it uses tests whether it comes from an official server. If it does, it's sent to the destination address, yet when it doesn't originate from a server indexed in the SPF record for the domain, it's rejected. Thus nobody will mask an email address to make it appear as if you're distributing spam messages. This approach is also called email spoofing.