Sender Policy Framework, or SPF, is a validation system, which is used to stop the so-called email spoofing where an email message can be sent from one email address, but to appear as being sent from a different one, frequently with the objective to scam the recipient someway. If SPF protection is activated for a domain name, a unique record is created 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 allowed to send legitimate messages from an e-mail address part of the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and in case its sending server is permitted, the message is forwarded to the target receiver. When, however, the sending server is not contained in the SPF record for the particular domain, the e-mail message won't be forwarded and it will be discarded. In case you use this service, it'll stop third parties from sending spam messages which look as if they have been sent from you.