SPF, which means Sender Policy Framework, is an email security system, which is designed to validate if an e-mail message was sent by a licensed server. Employing SPF protection for a domain name will prevent the forging of email addresses generated with the domain. In simple words: activating this feature for a domain name makes a special record in the Domain Name System (DNS) that contains the IP addresses of the servers which are allowed to send e-mails from mail boxes under the domain. As soon as this record propagates worldwide, it will exist on all of the DNS servers that direct the Internet traffic. When an email message is sent, the first DNS server it uses verifies whether it originates from an approved server. If it does, it is forwarded to the destination address, but when it doesn't originate from a server part of the SPF record for the domain, it's rejected. Thus nobody can mask an e-mail address to make it appear as if you are sending spam messages. This technique is also referred to as email spoofing.