Sender Policy Framework, or SPF, is a validation system, which is intended to stop the so-called email spoofing where an email message is sent from one e-mail, but to appear as being sent from another, typically with the purpose to fraud the recipient someway. When SPF protection is enabled for a domain name, a special record is created for it in the Domain Name System and all the DNS servers worldwide receive it. The record includes all e-mail servers that are allowed to send valid messages from an address part of the domain. When an email is sent, the very first DNS server it goes to checks the SPF record and when the sending server is permitted, the message is forwarded to the target receiver. In case, however, the sending server is not contained in the SPF record for the particular domain, the e-mail message will not be forwarded and it will be discarded. When you employ this solution, it'll stop third parties from sending spam messages that look as if they have been sent from you.
