SPF, which stands for Sender Policy Framework, is an e-mail security system, which is used to verify whether an email message was sent by a certified server. Using SPF protection for a particular domain will stop the forging of emails generated with the domain. In simple words: activating this function for a domain creates a special record in the Domain Name System (DNS) which contains the IP addresses of the servers that are permitted to send email messages from mailboxes under the domain. As soon as this record propagates worldwide, it will exist on all DNS servers that route the Internet traffic. Every time some email message is sent, the initial DNS server it uses checks if it originates from an authorized server. When it does, it is sent to the destination address, however if it doesn't come from a server listed in the SPF record for the domain, it's rejected. Thus nobody will mask an email address and make it look as if you're distributing spam. This approach is also known as email spoofing.