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 can be sent from one email, but to seem as being sent from a different one, ordinarily with the idea to scam the recipient for some reason. If SPF protection is activated for a domain, a unique record is created for it in the Domain Name System and all DNS servers around the world have it. The record includes all the email servers that are allowed to send authentic messages from an e-mail address under the domain. When a message is sent, the very first DNS server it encounters verifies the SPF record and in case the sending server is permitted, the message is sent to the target receiver. If, however, the sending server is not present in the SPF record for the given domain, the email message will not be forwarded and it'll be removed. Whenever you use this solution, it will prevent third parties from sending spam e-mails that look as if they have been sent by you.