Sender Policy Framework, or SPF, is a validation system, that is designed to stop the so-called e-mail spoofing where an email message is sent from one email, but to seem as being sent from another one, usually with the objective to fraud the recipient in some way. If SPF protection is activated for a domain, a special record is made for it in the Domain Name System and all the DNS servers around the world have it. The record includes all of the email servers that are permitted to send legitimate messages from an email address part of the domain. When a message is sent, the first DNS server it encounters verifies the SPF record and if its sending server is authorized, the message is forwarded to the targeted destination. If, however, the sending server is not included in the SPF record for the given domain, the email message won't be submitted and it will be removed. Whenever you use this service, it will prevent third parties from sending spam which appear to have been sent by you.