Sender Policy Framework, or SPF, is a validation system, that is intended to stop the so-called e-mail spoofing where an email message is sent from one email address, but to seem as being sent from another, generally with the idea to scam the recipient in some way. When SPF protection is activated for a domain name, a special record is made for it in the Domain Name System and all the DNS servers globally have it. The record includes all the e-mail servers that are allowed to send valid messages from an email address under the domain. When an e-mail is sent, the very first DNS server it goes to verifies the SPF record and if its sending server is permitted, the message is forwarded to the targeted destination. When, however, the sending server is not included in the SPF record for the specified domain, the email message won't be forwarded and it'll be removed. Whenever you use this solution, it'll prevent third parties from sending spam emails that seem to have been sent by you.