Sender Policy Framework, or SPF, is a verification system, that is used to stop the so-called e-mail spoofing where an e-mail message can be sent from one e-mail, but to look as being sent from another one, ordinarily with the objective to scam the recipient for some reason. When SPF protection is activated for a domain, a unique record is created for it in the Domain Name System and all of the DNS servers around the world receive it. The record contains all of the e-mail servers that are allowed to send valid messages from an e-mail address under the domain. When an e-mail is sent, the very first DNS server it encounters checks the SPF record and if the sending server is authorized, the message is sent to the target receiver. When, however, the sending server doesn't exist in the SPF record for the given domain, the e-mail message will not be forwarded and it'll be discarded. When you use this solution, it will prevent third parties from sending spam e-mails that seem to have been sent by you.