Sender Policy Framework, or SPF, is a verification system, that is used to prevent the so-called e-mail spoofing where an e-mail message can be sent from one address, but to appear as being sent from a different, generally with the idea to fraud the recipient someway. If SPF protection is enabled for a domain, an exclusive record is created for it in the Domain Name System and all DNS servers globally receive it. The record contains all of the e-mail servers that are allowed to send valid messages from an address within the domain. When an email is sent, the first DNS server it encounters checks the SPF record and in case the sending server is permitted, the message is forwarded to the targeted receiver. In case, however, the sending server doesn't exist in the SPF record for the specified domain, the message won't be forwarded and it'll be discarded. In the event that you use this solution, it will stop third parties from sending spam e-mails which appear to have been sent from you.