Sender Policy Framework, or SPF, is a verification system, that is intended to stop the so-called e-mail spoofing where an email message can be sent from one address, but to appear as being sent from another, generally with the idea to scam the recipient someway. If SPF protection is activated for a domain, a special record is made for it in the Domain Name System and all of the DNS servers around the world receive it. The record includes all email servers that are allowed to send authentic messages from an address part of the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and in case its sending server is authorized, the message is forwarded to the targeted destination. If, however, the sending server is not present in the SPF record for the given domain, the e-mail message won't be sent and it will be removed. Whenever you use this solution, it'll prevent third parties from sending spam messages that appear to have been sent by you.