Sender Policy Framework, or SPF, is a validation system, which is designed to stop the so-called e-mail spoofing where an e-mail message can be sent from one e-mail, but to appear as being sent from a different, often with the idea to fraud the recipient for some reason. If SPF protection is activated for a domain name, a unique record is generated for it in the Domain Name System and all of the DNS servers around the world receive it. The record features all of the e-mail servers that are permitted to send valid messages from an address under the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and when its sending server is authorized, the message is sent to the target receiver. In case, however, the sending server is not contained in the SPF record for the specified domain, the email message will not be sent and it'll be removed. If you employ this service, it'll prevent third parties from sending spam that appear to have been sent from you.