SPF, which means Sender Policy Framework, is an email security system, that is used to verify if an email message was sent by a certified server. Using SPF protection for a domain will stop the counterfeiting of email addresses created with the domain. In simple words: enabling this attribute for a domain makes a special record in the Domain Name System (DNS) which contains the IP of the servers which are allowed to send e-mails from mailboxes under the domain. When this record propagates worldwide, it will exist on all the DNS servers that route the Internet traffic. Whenever some e-mail message is sent, the initial DNS server it uses verifies if it originates from an approved server. In the event it does, it is forwarded to the destination address, yet if it doesn't come from a server part of the SPF record for the particular domain, it's rejected. In this way nobody can mask an email address and make it look as if you are distributing spam messages. This approach is also called email spoofing.