Sender Policy Framework, or SPF, is a verification system, which is used to stop the so-called email spoofing where an e-mail message is sent from one address, but to seem as being sent from a different, often with the purpose to fraud the recipient for some reason. When SPF protection is activated for a domain, a unique record is made for it in the Domain Name System and all DNS servers globally get it. The record includes all the e-mail servers that are permitted to send valid messages from an email address under the domain. When a message is sent, the very first DNS server it goes to checks the SPF record and in case the sending server is permitted, the message is sent to the target destination. When, however, the sending server is not present in the SPF record for the particular domain, the e-mail message won't be submitted and it'll be discarded. In the event that you use this service, it will stop third parties from sending spam which look as if they have been sent from you.