Sender Policy Framework, or SPF, is a validation system, that is designed to prevent the so-called email spoofing where an email message is sent from one e-mail, but to appear as being sent from a different, typically with the idea to scam the recipient for some reason. When SPF protection is activated for a domain, a specific record is generated for it in the Domain Name System and all the DNS servers globally receive it. The record includes all email servers that are allowed to send authentic messages from an e-mail address within the domain. When an e-mail is sent, the first DNS server it encounters verifies the SPF record and if the sending server is permitted, the message is forwarded to the targeted receiver. If, however, the sending server is not included in the SPF record for the particular domain, the email message won't be submitted and it'll be discarded. In case you employ this service, it will prevent third parties from sending spam messages which appear to have been sent from you.