Sender Policy Framework, or SPF, is a validation system, which is designed to prevent the so-called e-mail spoofing where an email message is sent from one address, but to seem as being sent from another one, usually with the objective to scam the recipient someway. When SPF protection is activated for a domain name, a unique 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 of the mail servers that are permitted to send legitimate messages from an address part of the domain. When a message is sent, the first DNS server it encounters checks the SPF record and if the sending server is authorized, the message is sent to the targeted destination. When, however, the sending server is not included in the SPF record for the given domain, the message will not be submitted and it will be discarded. If you employ this service, it will prevent third parties from sending spam messages that seem to have been sent by you.