Sender Policy Framework, or SPF, is a verification system, which is intended to prevent the so-called e-mail spoofing where an email message is sent from one e-mail, but to look as being sent from another one, usually with the objective to fraud the recipient in some way. When SPF protection is activated for a domain, a special record is made for it in the Domain Name System and all of the DNS servers around the world have it. The record features all e-mail servers that are allowed to send valid messages from an address part of the domain. When an email is sent, the first DNS server it encounters verifies the SPF record and when its sending server is permitted, the message is sent to the targeted receiver. When, however, the sending server doesn't exist in the SPF record for the given domain, the e-mail message will not be submitted and it will be removed. Whenever you use this service, it will prevent third parties from sending spam emails that seem to have been sent from you.