Sender Policy Framework, or SPF, is a validation system, that is employed to prevent the so-called e-mail spoofing where an email message can be sent from one e-mail, but to look as being sent from another, usually with the objective to fraud the recipient for some reason. If SPF protection is activated for a domain name, a specific record is generated for it in the Domain Name System and all the DNS servers around the world receive it. The record contains all email servers that are allowed to send authentic messages from an address part of the domain. When an email is sent, the very first DNS server it encounters checks the SPF record and in case its 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 sent and it'll be discarded. Whenever you employ this service, it'll stop third parties from sending spam that appear to have been sent by you.