Sender Policy Framework, or SPF, is a verification system, that is intended to stop the so-called email spoofing where an email message can be sent from one e-mail address, but to look as being sent from another one, frequently with the idea to scam the recipient in some way. When SPF protection is activated for a domain, a unique record is made for it in the Domain Name System and all DNS servers around the world have it. The record includes all the mail servers that are permitted to send valid messages from an e-mail address under the domain. When a message is sent, the very first DNS server it encounters verifies the SPF record and in case its sending server is permitted, the message is sent to the target destination. In case, however, the sending server is not present in the SPF record for the specified domain, the e-mail message won't be sent and it'll be discarded. When you use this solution, it'll prevent third parties from sending spam messages that look as if they have been sent from you.