SPF, which is short for Sender Policy Framework, is an email security system, which is employed to verify if an email message was sent by an authorized server. Using SPF protection for a domain will prevent the faking of email addresses generated with the domain. In simple words: enabling this attribute for a domain generates a special record in the Domain Name System (DNS) which includes the IP addresses of the servers which are allowed to send e-mails from mailboxes using the domain. When this record propagates globally, it exists on all of the DNS servers that route the Internet traffic. Every time a new email message is sent, the first DNS server it uses checks whether it originates from an authorized server. In the event it does, it's forwarded to the destination address, yet if it does not originate from a server indexed in the SPF record for the domain, it's rejected. In this way nobody will be able to mask an e-mail address to make it look as if you're distributing spam messages. This method is also termed email spoofing.