If your e-mail program sends a HTTP request for an image based on an "img" tag in a HTML-formatted e-mail, it can get tracked based on the URL. Many e-mail cli

If your e-mail program sends a HTTP request for an image based on an "img" tag in a HTML-formatted e-mail, it can get tracked based on the URL. Many e-mail clients will not show images from e-mail addresses that are not in your contacts list for this reason (for example, Thunderbird). They make the user click a button to make the decision to proceed with the image download an explicit action.