Sender Policy Framework, or SPF, is a validation system, which is employed to prevent the so-called e-mail spoofing where an e-mail message is sent from one email, but to seem as being sent from a different one, often with the objective to fraud the recipient in some way. When SPF protection is activated for a domain name, a special record is generated for it in the Domain Name System and all DNS servers around the world have it. The record includes all of the email servers that are allowed to send valid messages from an email address under the domain. When a message is sent, the very first DNS server it encounters verifies the SPF record and if the sending server is permitted, the message is sent to the target receiver. In case, however, the sending server is not present in the SPF record for the particular domain, the email message won't be forwarded and it'll be discarded. Whenever you employ this service, it'll stop third parties from sending spam e-mails which seem to have been sent by you.