SPF - DNS Record

(Sender Policy Framework). A SPF is an e-mail authentication system that verifies that the message came from an authorized mail server. SPF is designed to detect messages from spammers and phishers who falsify the sender's IP address in the e-mail header. SPF is an extension to the SMTP mail protocol. The DNS system identifies the IP address of a receiving mail server with a line of text in the DNS database known as an MX record. DNS also supports a "reverse MX" record, which identifies the sending mail server and is used by SPF. When an e-mail message is received, the mail server checks the SPF record in the DNS to see if it matches the actual IP address of the message.