> ## Documentation Index
> Fetch the complete documentation index at: https://docs.reelevant.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Email Client Caching and Proxies

> Understand how inbox proxies and caching affect open-time rendering

## 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

| Client                        | Caches or pre-fetches images? | Behaviour                                                                                                                                 | How Reelevant identifies it                                           |
| ----------------------------- | ----------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------- |
| Gmail image proxy             | No                            | Routes images through Google's proxy, but honours the Runner's no-cache headers, so the proxy refetches instead of serving a cached copy. | `GmailImageProxy` in the user agent.                                  |
| Apple Mail Privacy Protection | Yes                           | Proxies and caches images soon after delivery, even before a manual open.                                                                 | `Apple Mail Proxy`, `Apple Mail`, or a bare `Mozilla/5.0` user agent. |
| Outlook web                   | Sometimes                     | Webmail that can serve images through a caching proxy.                                                                                    | `Outlook` user agent, or an `outlook`/`office`/`live`.com referer.    |
| Outlook desktop               | No                            | Fetches at open time and honours the Runner's no-cache headers.                                                                           | `Outlook` user agent.                                                 |
| Outlook (enterprise)          | Depends on IT setup           | Security tooling can pre-fetch or cache images depending on the organisation's configuration. Reelevant identifies it as Outlook.         | Detected as `Outlook`; no dedicated signal.                           |
| Yahoo Mail                    | Often                         | Webmail that can serve images through a caching proxy.                                                                                    | Yahoo webmail referer.                                                |
| Orange Mail                   | No                            | Webmail detected by referer; fetches at open time.                                                                                        | Orange webmail referer.                                               |
| SFR Mail                      | No                            | Webmail detected by referer; fetches at open time.                                                                                        | SFR webmail referer.                                                  |

## What Reelevant does

The Runner marks every response as non-cacheable, sending `Cache-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.

## Impact on open-time features

| Feature             | What can go wrong                                                                                 | Mitigation                                                                                                          |
| ------------------- | ------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------- |
| Live Polling        | The percentage can freeze at pre-fetch time, so it reflects fetch time rather than the true open. | Non-cacheable responses and a fresh fetch reduce staleness, but aggressive proxy caching can still skew the figure. |
| Countdown           | A cached rendered image can freeze the timer and show an older time.                              | Non-cacheable responses help, but proxy caching can still show stale content.                                       |
| Any open-time value | The image can show earlier data than the recipient expects.                                       | Treat the image as a fetched snapshot when inbox proxies are involved.                                              |

## Related pages

* [Live Polling](/advanced-guide/workflows/data-nodes/live-polling)
* [Data Nodes](/advanced-guide/workflows/data-nodes)
* [Countdown Component](/product-guide/contents/components/countdown)