Sender Policy Framework, or SPF, is a verification system, which is employed to stop the so-called email spoofing where an email message can be sent from one email address, but to appear as being sent from a different one, frequently with the purpose to scam the recipient in some way. When SPF protection is enabled for a domain, a specific record is made for it in the Domain Name System and all the DNS servers globally get it. The record includes all e-mail servers that are permitted to send valid messages from an e-mail address part of the domain. When a message is sent, the very first DNS server it goes to checks the SPF record and when its sending server is authorized, the message is sent to the target receiver. 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 removed. In case you employ this solution, it will prevent third parties from sending spam messages that seem to have been sent by you.