Sender Policy Framework, or SPF, is a verification system, which is employed to prevent the so-called e-mail spoofing where an email message can be sent from one e-mail, but to seem as being sent from another, frequently with the purpose to scam the recipient for some reason. When SPF protection is activated for a domain, a special record is generated for it in the Domain Name System and all the DNS servers around the world have it. The record features all e-mail servers that are permitted to send legitimate messages from an e-mail address within the domain. When a message is sent, the very first DNS server it goes to checks the SPF record and when the sending server is authorized, the message is sent to the target destination. If, however, the sending server is not present in the SPF record for the specified domain, the email message won't be submitted and it will be discarded. If you use this solution, it'll prevent third parties from sending spam messages that look as if they have been sent from you.