SPF, which is short for Sender Policy Framework, is an email security system, that is designed to verify if an e-mail message was sent by an authorized server. Employing SPF protection for a given domain will prevent the forging of emails made with the domain. In layman's terms: enabling this attribute for a domain name makes a special record in the Domain Name System (DNS) which includes the IP of the servers that are permitted to send email messages from mailboxes using the domain. Once this record propagates worldwide, it exists on all the DNS servers that route the Internet traffic. Any time some e-mail message is sent, the first DNS server it goes through verifies whether it comes from an approved server. When it does, it's sent to the destination address, however when it does not come from a server indexed in the SPF record for the particular domain, it's rejected. Thus nobody will be able to mask an e-mail address and make it look as if you are distributing spam. This method is also called email spoofing.