Sender Policy Framework, or SPF, is a validation system, which is employed to stop the so-called e-mail spoofing where an e-mail message is sent from one email address, but to look as being sent from a different one, frequently with the objective to fraud the recipient someway. When SPF protection is enabled for a domain, a special record is made for it in the Domain Name System and all of the DNS servers around the world get it. The record features all mail servers that are allowed to send legitimate messages from an e-mail address under the domain. When a message is sent, the very first DNS server it encounters verifies the SPF record and when its sending server is authorized, the message is sent to the target receiver. If, however, the sending server is not included in the SPF record for the given domain, the e-mail message won't be sent and it will be discarded. In case you use this solution, it'll stop third parties from sending spam which look as if they have been sent from you.