Sender Policy Framework, or SPF, is a validation system, that is designed to prevent the so-called e-mail spoofing where an email message can be sent from one e-mail address, but to look as being sent from a different, frequently with the objective to fraud the recipient for some reason. When SPF protection is enabled for a domain name, a unique record is made for it in the Domain Name System and all of the DNS servers around the world have it. The record features all of the e-mail servers that are allowed to send legitimate messages from an address under the domain. When a message is sent, the first DNS server it goes to checks the SPF record and when its sending server is permitted, the message is sent to the target receiver. In case, however, the sending server doesn't exist in the SPF record for the specified domain, the message won't be sent and it will be discarded. If you employ this solution, it'll stop third parties from sending spam that look as if they have been sent by you.