SPF, which stands for Sender Policy Framework, is an e-mail security system, which is designed to validate whether an email message was sent by an official server. Using SPF protection for a domain name will prevent the counterfeiting of emails created with the domain. In simple words: activating this function for a domain creates a particular record in the Domain Name System (DNS) which includes the IP addresses of the servers which 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 route the Internet traffic. Whenever an email message is sent, the first DNS server it goes through checks whether it comes from an approved server. If it does, it is forwarded to the destination address, however if it doesn't come from a server part of the SPF record for the particular domain, it's discarded. In this way nobody will mask an e-mail address to make it appear as if you're sending spam messages. This technique is also known as email spoofing.