Sender Policy Framework, or SPF, is a verification system, that is employed to prevent the so-called e-mail spoofing where an email message is sent from one e-mail, but to appear as being sent from a different one, typically with the objective to scam the recipient for some reason. If SPF protection is activated for a domain, a special record is created for it in the Domain Name System and all DNS servers around the world get it. The record features all mail servers that are permitted to send valid messages from an address within the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and if its sending server is permitted, the message is forwarded to the targeted receiver. In case, however, the sending server is not present in the SPF record for the specified domain, the email message won't be forwarded and it'll be removed. In the event that you use this solution, it will stop third parties from sending spam emails which seem to have been sent from you.