Sender Policy Framework, or SPF, is a verification system, that is used to prevent the so-called email spoofing where an email message is sent from one address, but to look as being sent from a different one, generally with the purpose to scam 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 DNS servers globally have it. The record contains all the e-mail servers that are allowed to send valid messages from an e-mail address within the domain. When a message is sent, the first DNS server it goes to verifies the SPF record and if the sending server is authorized, the message is sent to the targeted destination. In case, however, the sending server is not present in the SPF record for the specified domain, the message won't be forwarded and it'll be discarded. Whenever you employ this solution, it'll stop third parties from sending spam emails that look as if they have been sent by you.