Sender Policy Framework, or SPF, is a validation system, which is intended to prevent the so-called e-mail spoofing where an e-mail message is sent from one address, but to look as being sent from another, typically with the idea to scam the recipient in some way. If SPF protection is enabled for a domain, a specific record is made for it in the Domain Name System and all of the DNS servers around the world get it. The record contains all of the mail servers that are permitted to send valid messages from an e-mail address under the domain. When an email is sent, the first DNS server it encounters verifies the SPF record and in case the sending server is permitted, the message is sent to the target destination. When, however, the sending server doesn't exist in the SPF record for the given domain, the e-mail message will not be sent and it'll be removed. Whenever you employ this service, it'll prevent third parties from sending spam e-mails that look as if they have been sent by you.