Sender Policy Framework, or SPF, is a verification system, which is used to stop the so-called e-mail spoofing where an e-mail message can be sent from one email address, but to appear as being sent from a different, usually with the purpose to fraud the recipient for some reason. When SPF protection is enabled for a domain name, a special record is generated for it in the Domain Name System and all of the DNS servers worldwide have it. The record features all the mail servers that are allowed to send valid messages from an e-mail address under the domain. When a message is sent, the first DNS server it encounters verifies the SPF record and if the sending server is permitted, the message is forwarded to the target destination. In case, however, the sending server is not contained in the SPF record for the specified domain, the e-mail message won't be submitted and it will be discarded. In case you employ this service, it will prevent third parties from sending spam which seem to have been sent by you.