SPF, which is an acronym for Sender Policy Framework, is an email security system, which is designed to verify if an email message is sent by an authorized server. Using SPF protection for a domain will prevent the counterfeiting of emails created with the domain. In simple words: activating this function for a domain makes a special record in the Domain Name System (DNS) which includes the IP of the servers which are allowed to send e-mail messages from mailboxes using the domain. When this record propagates worldwide, it will exist on all the DNS servers that direct the Internet traffic. Whenever a new e-mail message is sent, the first DNS server it goes through verifies if it originates from an authorized server. When it does, it's forwarded to the destination address, but when it doesn't come from a server part of the SPF record for the particular domain, it is discarded. In this way nobody will mask an email address and make it appear as if you're e-mailing spam messages. This technique is also referred to as email spoofing.