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 e-mail, but to seem as being sent from a different, typically with the idea to fraud the recipient in some way. If SPF protection is activated for a domain, a specific record is generated for it in the Domain Name System and all the DNS servers globally get it. The record contains all the email servers that are permitted to send valid messages from an address under the domain. When an e-mail is sent, the very first DNS server it encounters verifies the SPF record and when the sending server is permitted, the message is forwarded to the target destination. If, however, the sending server is not present in the SPF record for the given domain, the email message won't be submitted and it'll be removed. If you employ this service, it will prevent third parties from sending spam messages that appear to have been sent by you.