Sender Policy Framework, or SPF, is a verification system, which is employed to prevent the so-called e-mail spoofing where an e-mail message is sent from one e-mail address, but to appear as being sent from another one, often with the idea to scam the recipient someway. If SPF protection is enabled for a domain, a special record is created for it in the Domain Name System and all DNS servers around the world receive it. The record includes all of the email servers that are allowed to send valid messages from an email address under the domain. When an e-mail is sent, the first DNS server it goes to verifies the SPF record and in case the sending server is permitted, the message is forwarded to the target destination. When, however, the sending server is not included in the SPF record for the specified domain, the e-mail message won't be forwarded and it'll be removed. In the event that you use this service, it'll prevent third parties from sending spam messages that look as if they have been sent from you.