Sender Policy Framework, or SPF, is a validation system, that is intended to prevent the so-called email spoofing where an email message can be sent from one e-mail address, but to appear as being sent from a different one, generally with the objective to scam the recipient someway. If SPF protection is enabled for a domain, a unique record is created for it in the Domain Name System and all of the DNS servers worldwide have it. The record contains all the mail servers that are permitted 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 when the sending server is permitted, the message is sent to the target destination. In case, however, the sending server is not included in the SPF record for the given domain, the message won't be sent and it will be discarded. In the event that you use this service, it will prevent third parties from sending spam that appear to have been sent from you.