SPF, which stands for Sender Policy Framework, is an email security system, that is used to validate if an email message was sent by an official server. Using SPF protection for a given domain name will prevent the faking of email addresses generated with the domain. In simple words: enabling this feature for a domain makes a specific record in the Domain Name System (DNS) which contains the IP addresses of the servers that are allowed to send email messages from mailboxes under the domain. As soon as this record propagates globally, it exists on all of the DNS servers that direct the Internet traffic. Every time some e-mail message is sent, the initial DNS server it uses tests if it comes from an accredited server. When it does, it's forwarded to the destination address, however when it does not originate from a server indexed in the SPF record for the particular domain, it is discarded. Thus nobody will be able to mask an e-mail address to make it appear as if you are distributing spam messages. This technique is also identified as email spoofing.