Sender Policy Framework, or SPF, is a verification system, that is designed to stop the so-called email spoofing where an email message can be sent from one e-mail, but to look as being sent from a different one, usually with the objective to scam the recipient in some way. When SPF protection is enabled for a domain, a unique 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 legitimate messages from an address under the domain. When an e-mail is sent, the first DNS server it encounters checks the SPF record and in case its sending server is permitted, the message is sent to the target receiver. When, however, the sending server is not included in the SPF record for the particular domain, the email message will not be forwarded and it'll be removed. If you employ this solution, it'll stop third parties from sending spam emails which seem to have been sent by you.