Sender Policy Framework, or SPF, is a verification system, which is employed to prevent the so-called e-mail spoofing where an email message is sent from one email address, but to seem as being sent from another one, generally with the objective to fraud the recipient someway. When SPF protection is activated for a domain name, a specific record is created for it in the Domain Name System and all of the DNS servers globally get it. The record contains all of the e-mail servers that are permitted to send authentic messages from an email address within the domain. When an e-mail is sent, the very first DNS server it goes to checks the SPF record and in case its sending server is permitted, the message is forwarded to the target receiver. If, however, the sending server is not included in the SPF record for the specified domain, the message won't be forwarded and it will be removed. If you use this service, it'll stop third parties from sending spam that appear to have been sent from you.