Sender Policy Framework, or SPF, is a validation system, that is employed to stop the so-called email spoofing where an e-mail message is sent from one e-mail, but to look as being sent from a different one, generally with the objective to scam the recipient in some way. If SPF protection is activated for a domain name, a unique record is created for it in the Domain Name System and all the DNS servers worldwide get it. The record includes all email servers that are permitted 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 when its sending server is authorized, the message is forwarded to the targeted receiver. If, however, the sending server doesn't exist in the SPF record for the specified domain, the message will not be forwarded and it will be discarded. In case you employ this solution, it'll prevent third parties from sending spam messages which seem to have been sent by you.