Sender Policy Framework, or SPF, is a validation system, which is intended to prevent the so-called e-mail spoofing where an email message can be sent from one address, but to appear as being sent from a different, usually with the idea to fraud the recipient someway. If SPF protection is enabled for a domain name, a unique record is made for it in the Domain Name System and all of the DNS servers globally get it. The record contains all mail servers that are permitted to send valid messages from an e-mail address within the domain. When an email is sent, the very first DNS server it goes to checks the SPF record and if the sending server is authorized, the message is sent to the targeted destination. If, however, the sending server is not contained in the SPF record for the specified domain, the email message won't be submitted and it'll be discarded. If you employ this service, it'll prevent third parties from sending spam emails that seem to have been sent by you.