Overview
Email clients can fetch and cache images before a recipient opens the email. That means open-time rendering can reflect the fetch moment, not the exact open. This matters for features such as Live Polling and Countdown, where the image itself carries live content.Send-time and open-time rendering
Some inboxes and proxies pre-fetch images shortly after delivery. If they cache the image, the recipient can later see a frozen version. Other clients fetch at open time, which gives a fresher result when the Runner returns non-cacheable responses.Client behaviour
What Reelevant does
The Runner marks every response as non-cacheable, sendingCache-Control: no-cache, no-store, max-age=0, Pragma: no-cache, and Expires: -1.
That encourages clients that honour cache headers, such as the Gmail image proxy, to request a fresh image. Some clients, such as Apple Mail Privacy Protection, can still cache the image despite these headers.
When a click redirect happens, Reelevant preserves the previously identified client.
That matters because some proxies, such as Apple Mail Proxy, do not forward the same identifying headers on the click request.