SPF, which is an acronym for Sender Policy Framework, is an e-mail security system, that is employed to validate if an e-mail message was sent by an authorized server. Employing SPF protection for a given domain will prevent the faking of emails generated with the domain. In layman's terms: enabling this attribute for a domain makes a specific record in the Domain Name System (DNS) that contains the IP of the servers which are allowed to send emails from mailboxes under the domain. The moment this record propagates globally, it will exist on all DNS servers that direct the Internet traffic. When an e-mail message is sent, the initial DNS server it goes through tests whether it comes from an official server. In the event it does, it's forwarded to the destination address, however when it doesn't originate from a server part of the SPF record for the particular domain, it is rejected. Thus nobody will mask an email address to make it appear as if you're sending spam. This approach is also known as email spoofing.