Sender Policy Framework, or SPF, is a verification system, which is intended to stop the so-called email spoofing where an email message can be sent from one e-mail address, but to appear as being sent from another, often with the idea to fraud the recipient in some way. If SPF protection is enabled for a domain, a special record is generated for it in the Domain Name System and all the DNS servers worldwide have it. The record features all of the e-mail servers that are allowed to send authentic messages from an email address part of the domain. When a message is sent, the first DNS server it encounters verifies the SPF record and if the sending server is authorized, the message is forwarded to the target destination. In case, however, the sending server is not included in the SPF record for the particular domain, the message won't be forwarded and it'll be discarded. In the event that you use this solution, it'll stop third parties from sending spam e-mails which seem to have been sent by you.