SPF, which stands for Sender Policy Framework, is an email safety system, that is is intended to confirm whether an e-mail message was sent by a certified server. Using SPF protection for a domain will prevent the counterfeiting of email addresses created with the domain. In simple words: enabling this feature for a domain name generates a particular record in the Domain Name System (DNS) which includes the IP of the servers which are allowed to send e-mails from mail boxes using the domain. The moment this record propagates worldwide, it will exist on all the DNS servers that direct the Internet traffic. Any time a new e-mail message is sent, the initial DNS server it goes through verifies if it comes from an official server. When it does, it is forwarded to the destination address, but if it doesn't originate from a server part of the SPF record for the particular domain, it is discarded. Thus nobody will mask an email address to make it appear as if you're sending spam messages. This approach is also known as email spoofing.