Sender Policy Framework, or SPF, is a verification system, that is designed to prevent the so-called email spoofing where an email message is sent from one email, but to seem as being sent from another one, often with the objective to fraud the recipient in some way. If SPF protection is enabled for a domain, a special record is generated for it in the Domain Name System and all of the DNS servers around the world have it. The record contains all of the email servers that are permitted to send authentic messages from an email address within the domain. When a message is sent, the first DNS server it goes to verifies the SPF record and in case the sending server is permitted, the message is sent to the targeted receiver. When, however, the sending server doesn't exist in the SPF record for the specified domain, the email message will not be sent and it will be removed. If you employ this solution, it'll prevent third parties from sending spam which seem to have been sent by you.