Sender Policy Framework, or SPF, is a validation system, that is used to prevent the so-called e-mail spoofing where an e-mail message is sent from one e-mail, but to seem as being sent from another one, generally with the objective to scam the recipient someway. When SPF protection is activated for a domain name, an exclusive record is created for it in the Domain Name System and all of the DNS servers globally get it. The record features all of the email servers that are permitted to send authentic messages from an address part of the domain. When an email is sent, the first DNS server it goes to checks the SPF record and if the sending server is permitted, the message is forwarded to the targeted destination. When, however, the sending server is not contained in the SPF record for the specified domain, the message won't be submitted and it will be discarded. Whenever you use this service, it'll prevent third parties from sending spam which appear to have been sent by you.