Sender Policy Framework, or SPF, is a verification system, which is used to stop the so-called e-mail spoofing where an email message is sent from one address, but to look as being sent from another, frequently with the purpose to fraud the recipient for some reason. When SPF protection is activated for a domain name, an exclusive record is generated for it in the Domain Name System and all DNS servers around the world receive it. The record contains all of the mail servers that are permitted to send authentic messages from an e-mail address under the domain. When an e-mail is sent, the very first DNS server it encounters checks the SPF record and if the sending server is authorized, the message is sent to the targeted receiver. When, however, the sending server is not included in the SPF record for the given domain, the message will not be submitted and it'll be removed. Whenever you use this service, it will stop third parties from sending spam messages which seem to have been sent by you.