Sender Policy Framework, or SPF, is a verification system, that is used to prevent the so-called e-mail spoofing where an e-mail message is sent from one email address, but to appear as being sent from a different, often with the idea to fraud the recipient someway. If SPF protection is activated for a domain, a specific record is generated for it in the Domain Name System and all of the DNS servers worldwide have it. The record features all the e-mail servers that are permitted to send valid messages from an address part of the domain. When an email is sent, the first DNS server it goes to verifies the SPF record and in case the sending server is authorized, the message is sent to the target receiver. In case, however, the sending server doesn't exist in the SPF record for the given domain, the e-mail message will not be forwarded and it'll be discarded. Whenever you use this solution, it'll prevent third parties from sending spam messages which seem to have been sent by you.