Sender Policy Framework, or SPF, is a verification system, which is used to prevent the so-called e-mail spoofing where an e-mail message can be sent from one email address, but to appear as being sent from a different, typically with the purpose to scam 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 of the DNS servers globally get it. The record features all of the email servers that are permitted to send valid messages from an email address under the domain. When an e-mail is sent, the very first DNS server it goes to verifies the SPF record and if the sending server is authorized, the message is forwarded to the targeted destination. In case, however, the sending server is not present in the SPF record for the given domain, the e-mail message won't be submitted and it will be discarded. In case you use this service, it'll prevent third parties from sending spam emails that appear to have been sent by you.