Received emails are not displaying images correctly (.ashx suffix)

Question

Images embedded in HTML emails are referenced using .ashx URLs that return an HTTP 308 Permanent Redirect to /api/legacy-media/.... Chrome follows the redirect correctly, however Microsoft Outlook (New Outlook and Outlook on the web) does not display the images. The final endpoint returns 200 OK with Content-Type: image/png, so the image itself is valid. I'm aware that the sender (external to enterprise) could update the image URLs to reference the final /api/legacy-media/... endpoint directly, or change the redirect to a 301/302 if appropriate, however, I'm skeptical they will respond in a timely manner. Is there a workaround or a possible fix to this problem?

Answer 1

Hi @Andri

Based on your description, the image file itself appears to be valid because the final URL returns 200`` ``OK with Content-Type:`` ``image/png. The issue is likely related to how Outlook retrieves external images, especially when the image URL first returns a 308`` ``Permanent`` ``Redirect before reaching the actual image endpoint.

Outlook on the web and New Outlook may load external images through Outlook’s image protection/proxy service rather than behaving exactly like Chrome. Microsoft documents that Outlook uses external image protection to help protect user data by loading online images through an image proxy, and users can choose whether Outlook should use that service to load external images. Microsoft also documents that Outlook may block automatic picture downloads from the Internet by default for privacy and security reasons, including protection against tracking pixels and unsafe external content.

Because of that, even if Chrome follows the 308 redirect successfully, it does not necessarily confirm that Outlook’s image proxy will support the same redirect chain. In this scenario, the best permanent fix would still be on the sender/content-hosting side:

• Replace the .ashx image URLs in the HTML email with the final /api/legacy-media/... image URLs directly.
• Or change the redirect behavior to a more commonly supported redirect such as 301 or 302, if that is appropriate for the application.
• Ensure the image endpoint is publicly accessible without cookies, authentication headers, session state, or browser-only behavior.
• Ensure the final image response includes a correct image MIME type, for example image/png, and does not rely on scripts or dynamic request handling that an email client/proxy may reject.

As a recipient-side workaround, you can try the following, but these may not resolve a redirect-handling issue:

1. Use Download** **Pictures for that message if Outlook shows the option. Microsoft documents this as the supported way to unblock linked pictures for a trusted message.
2. Add the sender or sender domain to the Safe Senders list, if the sender is trusted. Microsoft documents this as a way to allow picture downloads from a particular sender or domain in classic Outlook.
3. Test the same message in classic Outlook, Outlook mobile, and another mailbox to confirm whether the issue is specific to New Outlook/OWA image handling.

If the images still do not load after those checks, there may not be a reliable recipient-side fix. The sender would need to modify the image URLs or redirect behavior.

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