Sender Policy Framework, or SPF, is a validation system, that is intended to stop the so-called email spoofing where an e-mail message is sent from one address, but to appear as being sent from a different, generally with the purpose to scam the recipient for some reason. If SPF protection is activated for a domain name, a specific record is made for it in the Domain Name System and all of the DNS servers around the world receive it. The record features all email servers that are allowed to send authentic messages from an e-mail address under the domain. When a message is sent, the first DNS server it encounters verifies the SPF record and in case the sending server is authorized, the message is sent to the target receiver. If, however, the sending server is not present in the SPF record for the given domain, the message won't be submitted and it'll be discarded. In case you use this solution, it will stop third parties from sending spam messages which seem to have been sent by you.