SPF, which is short for Sender Policy Framework, is an email security system, which is is intended to validate whether an email message was sent by a certified server. Employing SPF protection for a particular domain will prevent the forging of email addresses created with the domain. In layman's terms: enabling this attribute for a domain creates a special record in the Domain Name System (DNS) containing the IP addresses of the servers which are permitted to send e-mails from mail boxes using the domain. The moment this record propagates globally, it will exist on all the DNS servers that route the Internet traffic. Any time some e-mail message is sent, the first DNS server it uses tests if it comes from an approved server. If it does, it is sent to the destination address, but if it doesn't originate from a server listed in the SPF record for the particular domain, it is rejected. Thus nobody can mask an email address and make it look as if you are e-mailing spam messages. This method is also known as email spoofing.
