Sender Policy Framework, or SPF, is a verification system, that is designed to prevent the so-called email spoofing where an e-mail message is sent from one e-mail address, but to look as being sent from a different, ordinarily with the objective to scam the recipient in some way. When SPF protection is enabled for a domain name, a special record is made for it in the Domain Name System and all of the DNS servers worldwide have it. The record includes all of the mail servers that are permitted to send authentic messages from an e-mail address within the domain. When a message is sent, the very first DNS server it goes to verifies the SPF record and if the sending server is permitted, the message is forwarded to the targeted receiver. In case, however, the sending server is not included in the SPF record for the given domain, the e-mail message won't be sent and it'll be removed. Whenever you use this service, it'll prevent third parties from sending spam messages that seem to have been sent by you.