Sender Policy Framework, or SPF, is a verification system, that is used to stop the so-called email spoofing where an e-mail message can be sent from one email address, but to seem as being sent from another, generally with the purpose to scam the recipient for some reason. If SPF protection is activated for a domain, a specific record is created for it in the Domain Name System and all the DNS servers around the world have it. The record includes all the mail servers that are permitted to send authentic messages from an email address within the domain. When an email is sent, the first DNS server it goes to checks the SPF record and in case its sending server is permitted, the message is forwarded to the target receiver. When, however, the sending server is not present in the SPF record for the specified domain, the email message will not be forwarded and it'll be discarded. In the event that you use this solution, it'll stop third parties from sending spam messages that look as if they have been sent by you.