Sender Policy Framework, or SPF, is a validation system, which is designed to prevent the so-called email spoofing where an email message is sent from one e-mail, but to appear as being sent from another, generally with the objective to fraud the recipient in some way. When SPF protection is activated for a domain, a special record is created for it in the Domain Name System and all the DNS servers around the world get it. The record contains all of the mail servers that are permitted to send valid messages from an e-mail address within the domain. When an email is sent, the first DNS server it goes to verifies the SPF record and if the sending server is permitted, the message is forwarded to the target destination. In case, however, the sending server is not contained in the SPF record for the specified domain, the message won't be forwarded and it'll be discarded. When you use this solution, it will prevent third parties from sending spam messages which appear to have been sent from you.