Sender Policy Framework, or SPF, is a verification system, that is used to stop the so-called e-mail spoofing where an email message can be sent from one e-mail, but to look as being sent from a different one, frequently with the idea to fraud the recipient for some reason. When SPF protection is enabled for a domain, a unique record is made for it in the Domain Name System and all the DNS servers around the world have it. The record features all the mail servers that are allowed to send authentic messages from an email address part of the domain. When an e-mail is sent, the first DNS server it goes to checks the SPF record and when its sending server is permitted, the message is forwarded to the target destination. In case, however, the sending server doesn't exist in the SPF record for the given domain, the e-mail message won't be submitted and it'll be removed. In the event that you use this service, it will prevent third parties from sending spam e-mails that appear to have been sent by you.