The Sender Policy Framework (SPF) is an email-authentication technique which is used to prevent spammers from sending messages on behalf of your domain. With SPF an organization can publish authorized mail servers. Together with the DMARC related information, this gives the receiver (or receiving systems) information on how trustworthy the origin of an email is. SPF is, just like DMARC, a email authentication technique that uses DNS (Domain Name Service). This gives you, as an email sender, the ability to specify which email servers are permitted to send email on behalf of your domain.