Contrary to popular beliefs, gmail does not pre-fetch all the images. It fetches the images via a proxy the first time the user loads the email via gmail app or

Contrary to popular beliefs, gmail does not pre-fetch all the images. It fetches the images via a proxy the first time the user loads the email via gmail app or gmail web, and caches it for repeat opens. Also, there’s no proxying if the user uses a third party app (like the iPhone app). So open metrics are still fairly accurate since not many users open the same email multiple times. So why does gmail do this if it still allows the websites to track opens? Primarily to prevent IP address leak and to prevent the website owner from reading it's cookies on email opens (if opened on a browser), and/or cross-linking multiple emails for further tracking and linking identities.