Sender Policy Framework, or SPF, is a validation system, that is used to stop the so-called email spoofing where an e-mail message can be sent from one e-mail, but to appear as being sent from a different, often with the purpose to fraud the recipient for some reason. If SPF protection is activated for a domain name, a special 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 mail servers that are allowed to send authentic messages from an email address under the domain. When an email is sent, the first DNS server it encounters checks the SPF record and when the sending server is permitted, the message is sent to the targeted destination. In case, however, the sending server is not included in the SPF record for the specified domain, the message will not be sent and it'll be removed. Whenever you use this service, it will prevent third parties from sending spam messages that seem to have been sent by you.