Sender Authentication: What Is It, and How Can It Help You?

IF: Could you define Sender ID?
Guerra: Sender ID is a blend of SPF and Caller ID, a protocol written by Microsoft. Sender ID can be implemented to verify the same information as SPF and can also verify that the IP address used is allowed to send on behalf of the sender listed in the From address. Sender ID can verify information that is visible to the reader of the message as well as information intended for the ISP.