Sender Policy Framework, or SPF, is a validation system, that is employed to prevent the so-called email spoofing where an email message is sent from one address, but to appear as being sent from a different one, ordinarily with the purpose to fraud the recipient someway. When SPF protection is activated for a domain name, a unique record is created for it in the Domain Name System and all the DNS servers globally have it. The record includes all of the mail servers that are allowed to send valid messages from an email address part of the domain. When a message is sent, the first DNS server it goes to checks the SPF record and in case its sending server is authorized, the message is forwarded to the target receiver. If, however, the sending server is not present in the SPF record for the given domain, the e-mail message won't be sent and it'll be discarded. In the event that you use this solution, it will stop third parties from sending spam that seem to have been sent by you.