Electronic mail, often abbreviated as email or e-mail, is a method of exchanging digital messages, designed primarily for human use. An electronic mail message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually additional information is added, such as a subject header field. E-mail systems are based on a store-and-forward model in which e-mail computer server systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the e-mail infrastructure, typically an e-mail server, with a network-enabled device (e.g., a personal computer) for the duration of message submission or retrieval. Rarely is e-mail transmitted directly from one user's device to another's.

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You want to display the entire header of the incoming email. The method depends on your e-mail client. Search with Google "[email client type /google mail, yahoo, outlook.../] show originating IP" and see what you get.

With my gmail account there is a drop down menu that allows me to "show original" and then the header is displayed.