SPF, which means Sender Policy Framework, is an email protection system, that is is intended to verify whether an e-mail message was sent by an authorized server. Using SPF protection for a particular domain will prevent the faking of email addresses created with the domain. In simple words: enabling this feature for a domain creates a special record in the Domain Name System (DNS) containing the IP addresses of the servers which are allowed to send emails from mail boxes under the domain. As soon as this record propagates worldwide, it exists on all DNS servers that route the Internet traffic. Every time some e-mail message is sent, the initial DNS server it uses verifies if it originates from an authorized server. In the event it does, it's sent to the destination address, but if it does not come from a server indexed in the SPF record for the domain, it is rejected. Thus nobody will be able to mask an email address and make it look as if you're sending spam. This technique is also called email spoofing.