Sender Policy Framework, or SPF, is a validation system, which is employed to prevent the so-called email spoofing where an e-mail message can be sent from one address, but to look as being sent from a different, generally with the objective to fraud the recipient for some reason. When SPF protection is activated for a domain name, an exclusive record is generated for it in the Domain Name System and all the DNS servers around the world get it. The record includes all of the mail servers that are allowed to send legitimate messages from an address under the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and if the sending server is permitted, the message is forwarded to the targeted destination. When, however, the sending server is not present in the SPF record for the given domain, the message will not be submitted and it will be discarded. In the event that you employ this solution, it'll prevent third parties from sending spam emails which look as if they have been sent by you.