Sender Policy Framework, or SPF, is a verification system, that is employed to prevent the so-called email spoofing where an e-mail message is sent from one email address, but to seem as being sent from a different, often with the purpose to scam the recipient someway. When SPF protection is enabled for a domain, a special record is generated for it in the Domain Name System and all of the DNS servers around the world have it. The record includes all e-mail servers that are permitted to send legitimate messages from an e-mail address part of the domain. When a message 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 sent to the target destination. If, however, the sending server is not contained in the SPF record for the given domain, the email message won't be forwarded and it'll be removed. When you employ this solution, it'll stop third parties from sending spam messages which seem to have been sent by you.