SPF, which means Sender Policy Framework, is an e-mail security system, that is used to verify whether an e-mail message is sent by a certified server. Employing SPF protection for a domain will prevent the forging of emails generated with the domain. In layman's terms: enabling this feature for a domain makes a specific record in the Domain Name System (DNS) which includes the IP addresses of the servers which are permitted to send email messages from mailboxes using the domain. As soon as this record propagates worldwide, it exists on all of the DNS servers that direct the Internet traffic. Whenever some e-mail message is sent, the initial DNS server it uses verifies whether it comes from an accredited server. If it does, it's forwarded to the destination address, however when it does not originate from a server listed in the SPF record for the particular domain, it is rejected. Thus nobody will mask an e-mail address to make it look as if you're sending spam. This technique is also termed email spoofing.