Sender Policy Framework, or SPF, is a verification system, which is intended to prevent the so-called email spoofing where an email message can be sent from one email address, but to look as being sent from a different one, often with the purpose to fraud the recipient in some way. If SPF protection is activated for a domain name, a specific record is made for it in the Domain Name System and all DNS servers globally have it. The record contains all the mail servers that are allowed to send legitimate messages from an email address part of the domain. When an email is sent, the first DNS server it goes to checks the SPF record and if the sending server is permitted, the message is sent to the targeted destination. In case, however, the sending server is not contained in the SPF record for the specified domain, the e-mail message won't be forwarded and it will be removed. In case you employ this solution, it'll stop third parties from sending spam that look as if they have been sent from you.