Sender Policy Framework, or SPF, is a verification system, that is intended to stop the so-called email spoofing where an e-mail message can be sent from one email, but to appear as being sent from another one, typically with the purpose to scam the recipient for some reason. When SPF protection is enabled for a domain, a special record is generated for it in the Domain Name System and all DNS servers globally have it. The record features all the e-mail servers that are permitted to send legitimate messages from an email address within the domain. When an email is sent, the very first DNS server it encounters verifies the SPF record and in case the sending server is authorized, the message is forwarded to the target receiver. When, however, the sending server is not present in the SPF record for the particular domain, the message won't be submitted and it'll be removed. In case you use this solution, it'll stop third parties from sending spam emails that seem to have been sent by you.