Sender Policy Framework, or SPF, is a validation system, that is used to prevent the so-called email spoofing where an email message is sent from one e-mail, but to appear as being sent from another one, often with the objective to fraud the recipient someway. If SPF protection is activated for a domain, an exclusive record is made for it in the Domain Name System and all the DNS servers globally receive it. The record includes all of the mail servers that are allowed to send legitimate messages from an email address part of the domain. When an email is sent, the first DNS server it goes to verifies the SPF record and in case its sending server is authorized, the message is sent to the target destination. When, however, the sending server is not present in the SPF record for the given domain, the email message won't be sent and it will be discarded. When you use this service, it'll stop third parties from sending spam messages that appear to have been sent by you.