Sender Policy Framework, or SPF, is a validation system, which is designed to prevent the so-called e-mail spoofing where an email message can be sent from one e-mail address, but to appear as being sent from another one, often with the purpose to fraud the recipient someway. If SPF protection is activated for a domain name, an exclusive record is generated for it in the Domain Name System and all of the DNS servers globally receive it. The record includes all email servers that are allowed to send valid messages from an address under the domain. When an e-mail is sent, the first DNS server it encounters verifies the SPF record and if its sending server is permitted, the message is forwarded to the targeted destination. If, however, the sending server is not included in the SPF record for the given domain, the e-mail message will not be forwarded and it will be discarded. Whenever you use this service, it'll stop third parties from sending spam which appear to have been sent by you.