Sender Policy Framework, or SPF, is a validation system, which is employed to stop the so-called e-mail spoofing where an e-mail message can be sent from one e-mail, but to look as being sent from another one, frequently with the purpose to scam the recipient for some reason. When SPF protection is activated for a domain name, a specific record is made for it in the Domain Name System and all of the DNS servers globally have it. The record includes all of the email servers that are permitted to send valid messages from an e-mail address part of the domain. When an e-mail is sent, the first DNS server it encounters verifies the SPF record and if its sending server is authorized, the message is forwarded to the target destination. When, however, the sending server is not included in the SPF record for the given domain, the message won't be submitted and it'll be discarded. If you use this service, it will prevent third parties from sending spam e-mails which look as if they have been sent from you.