Sender Policy Framework, or SPF, is a validation system, that is intended to stop the so-called email spoofing where an email message can be sent from one email, but to look as being sent from a different one, often with the objective to fraud the recipient someway. If SPF protection is enabled for a domain name, a unique record is created for it in the Domain Name System and all the DNS servers worldwide receive it. The record contains all the e-mail servers that are allowed to send authentic messages from an email address part of the domain. When an e-mail is sent, the first DNS server it encounters verifies the SPF record and if the sending server is authorized, the message is sent to the target destination. If, however, the sending server is not contained in the SPF record for the particular domain, the e-mail message will not be forwarded and it will be discarded. In case you use this solution, it'll prevent third parties from sending spam messages which appear to have been sent by you.