Sender Policy Framework, or SPF, is a validation system, which is designed to prevent the so-called e-mail spoofing where an e-mail message can be sent from one email address, but to appear as being sent from a different, usually with the objective to scam the recipient someway. If SPF protection is enabled for a domain, a special record is created for it in the Domain Name System and all DNS servers around the world have it. The record features all of the e-mail servers that are allowed to send authentic messages from an email address under the domain. When an email is sent, the very first DNS server it goes to checks the SPF record and if the sending server is permitted, the message is forwarded to the targeted receiver. In case, however, the sending server is not included in the SPF record for the given domain, the e-mail message will not be forwarded and it'll be removed. In the event that you use this service, it will prevent third parties from sending spam messages that seem to have been sent by you.