Sender Policy Framework, or SPF, is a validation system, which is designed 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 another, frequently with the objective to fraud the recipient someway. When SPF protection is enabled for a domain, a unique record is made for it in the Domain Name System and all of the DNS servers globally get it. The record features all the mail servers that are permitted to send valid messages from an e-mail address part of the domain. When an e-mail is sent, the first DNS server it goes to checks the SPF record and when the sending server is authorized, the message is forwarded to the targeted receiver. When, however, the sending server is not contained in the SPF record for the given domain, the message won't be forwarded and it'll be discarded. In case you use this solution, it'll prevent third parties from sending spam messages which appear to have been sent by you.