Sender Policy Framework, or SPF, is a verification system, that is designed to stop the so-called email spoofing where an email message is sent from one email address, but to look as being sent from a different one, generally with the purpose to scam the recipient for some reason. If SPF protection is enabled for a domain, a special record is created for it in the Domain Name System and all of the DNS servers around the world get it. The record features all e-mail servers that are allowed to send valid messages from an 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 destination. When, however, the sending server is not contained in the SPF record for the given domain, the email message won't be forwarded and it'll be discarded. In the event that you use this solution, it will stop third parties from sending spam e-mails which appear to have been sent from you.