Sender Policy Framework, or SPF, is a verification system, that is designed to prevent the so-called e-mail spoofing where an email message is sent from one address, but to appear as being sent from another, generally with the objective to scam the recipient someway. If SPF protection is enabled for a domain, an exclusive record is made for it in the Domain Name System and all DNS servers worldwide get it. The record contains all the email servers that are allowed to send valid messages from an email address part of the domain. When a message is sent, the very first DNS server it encounters checks the SPF record and in case its sending server is permitted, the message is forwarded to the target receiver. In case, however, the sending server doesn't exist in the SPF record for the specified domain, the message will not be sent and it will be discarded. In case you employ this service, it will prevent third parties from sending spam messages which look as if they have been sent by you.