Sender Policy Framework, or SPF, is a verification system, that is employed to stop the so-called e-mail spoofing where an e-mail message is sent from one email, but to look as being sent from a different, usually with the purpose to fraud the recipient someway. If SPF protection is activated for a domain, a special record is made for it in the Domain Name System and all of the DNS servers worldwide receive it. The record features all the mail servers that are allowed to send authentic messages from an e-mail address within the domain. When an email is sent, the very first DNS server it encounters checks the SPF record and in case the sending server is permitted, the message is forwarded to the target receiver. If, however, the sending server is not included in the SPF record for the particular domain, the message will not be submitted and it'll be removed. If you use this service, it will stop third parties from sending spam emails which appear to have been sent by you.