SPF, which means Sender Policy Framework, is an e-mail security system, that is designed to confirm if an email message was sent by a certified server. Using SPF protection for a given domain will prevent the forging of emails created with the domain. In simple words: activating this feature for a domain name generates a special record in the Domain Name System (DNS) which includes the IP addresses of the servers which are allowed to send emails from mail boxes under the domain. The moment this record propagates worldwide, it exists on all the DNS servers that direct the Internet traffic. Whenever some e-mail message is sent, the initial DNS server it uses tests if it originates from an accredited server. In the event it does, it is forwarded to the destination address, however if it does not originate from a server indexed in the SPF record for the domain, it's discarded. Thus nobody can mask an e-mail address to make it appear as if you are sending spam. This technique is also called email spoofing.