Blog Content Workflows April 26, 2026 8 min read

Why Email Clients Block Images and What to Use Instead

Email images blocked by default in Outlook and Gmail means your design relies on invisible assets. Here is what still works and how to plan for it.

email images blockedemail client image loadingHTML emailemail alt textemail design fallback

Why Email Clients Block Images and What to Use Instead

Most desktop email clients block external images by default, including Outlook on Windows and many corporate Gmail environments. When images are blocked, your email renders with empty boxes and alt text strings. If your layout depends on images to convey meaning, blocked-image rendering breaks the email's message entirely.

Understanding which clients block images and why changes how you design the fallback state. The goal is not to make blocked images invisible — it is to make the email readable and persuasive even when no images load.

Which clients block

Email clients that block images by default in 2026

Outlook 2016, 2019, and 2021 on Windows block all external images until the user clicks 'Download Pictures.' This setting is on by default and affects corporate environments where IT policy enforces it. Outlook 365 in the desktop app follows the same behavior. Outlook on the web (OWA) loads images by default.

Gmail on Android and iOS loads images automatically via Google's image proxy cache. Desktop Gmail in a browser loads images. The corporate exception is Google Workspace accounts where the administrator has configured an image proxy policy — these rarely block images outright.

Apple Mail on macOS and iOS loads images with Mail Privacy Protection enabled, but the images load via Apple's proxy, not the user's IP. This means images appear to load for tracking purposes while actual user location is masked. Thunderbird blocks remote images by default. Yahoo Mail and Outlook.com (web) load images.

Blocks by default

Outlook 2016/2019/2021 (desktop), Thunderbird, some Lotus Notes environments.

Loads via proxy

Gmail (Google proxy), Apple Mail (Apple Privacy Relay) — images load but IP is hidden.

Loads directly

Outlook.com (web), Yahoo Mail, Gmail in browser without Workspace policy.

Impact

What blocked images do to your email layout

When images are blocked in Outlook, the img element renders as a box with the dimensions you specified (if you specified them) or as a collapsed 16px-tall line. If you used images for spacing, the layout shifts. If the hero image was full-width and 200px tall, Outlook shows an empty 600×200 box with a broken-image icon in the corner.

Buttons built from images break completely. The call-to-action becomes invisible. This is why HTML email best practice has recommended VML buttons for Outlook since the early 2010s. Any essential content that lives inside an image — product names, prices, CTA copy — is invisible to users who block images.

The blocked-image state is not an edge case. In corporate B2B email campaigns, Outlook-on-Windows open rates can represent 30-40% of your audience depending on industry. Designing only for the images-loaded state means designing for less than the full audience.

Alt text

Writing alt text that carries the message when images are blocked

Alt text in email is not just for accessibility — it is the content that blocked-image users see. Write alt text as if it is the only thing the subscriber will read. For a hero image showing a product launch announcement, alt='Image' is useless. Alt='Announcing the new API dashboard — live today' carries the message.

Outlook renders alt text in the default system font inside the broken-image box. You can style it with the font attributes on the img element, but support is inconsistent. The more reliable approach is to never put essential information exclusively inside an image. Use HTML text for headlines and CTAs, and use images only as visual reinforcement.

Implementation text

<!-- Alt text that carries meaning -->
<img
  src="https://fallback.pics/api/v1/banner/600x200
    ?text=Announcing+the+new+API+dashboard&theme=purple"
  width="600"
  height="200"
  alt="Announcing the new API dashboard — live today"
  style="display:block;border:0;"
/>

<!-- Use HTML text for critical CTA, not an image button -->
<table>
  <tr>
    <td bgcolor="#7C3AED" style="border-radius:4px;padding:12px 24px;">
      <a href="https://app.example.com" style="color:#fff;text-decoration:none;font-weight:600;">
        Open Dashboard
      </a>
    </td>
  </tr>
</table>

Design strategy

Designing email layouts that work with and without images

The safe email design pattern puts all informational content in HTML text and uses images only for brand personality and visual polish. The hero image sets the tone but the headline below it carries the message. The product photo is nice to have but the product name, price, and CTA are plain HTML.

Background colors on table cells are a reliable fallback for images in layout-critical areas. A purple table cell with white HTML text reads well even when the background image on that cell fails to load. Test your email in Outlook's image-blocking mode before sending to see exactly what blocked-image subscribers experience.

For transactional emails (order confirmations, password resets), the content is functional rather than persuasive, so blocked images matter less. For marketing emails, especially those promoting visual products like apparel or furniture, blocked images can significantly reduce the email's effectiveness.

URL-based images

When URL-based placeholder images help in email

URL-based images from fallback.pics do not solve the blocked-images problem because they are still external images. What they do solve is the 'image never uploaded' problem and the 'hosting domain went down' problem. They also produce correct dimensions reliably, which matters for Outlook's broken-image box rendering.

When you specify a fallback.pics URL in the img src, you know the URL will return a valid image at the exact dimensions you requested. The broken-image box in Outlook will have the correct size, and the alt text will be displayed at those dimensions rather than collapsing. This is marginally better than a 404 response from a deleted S3 object.

Testing

Simulating blocked images during development

In Outlook on Windows, go to File → Options → Trust Center → Trust Center Settings → Automatic Download and check 'Don't download pictures automatically.' This simulates the default corporate experience. Check the email in this mode before every campaign send.

In Litmus and Email on Acid, image blocking previews are available as a rendering variant alongside regular previews. Set blocked-images as a required test case in your QA checklist. Thunderbird's image blocking is in Preferences → Privacy → Block remote content.

Resources

What to standardize before shipping

Outlook 2016-2021 on Windows blocks external images by default — this affects a significant share of B2B email audiences.
Write alt text as a content fallback, not a description: it must carry the message when images are invisible.
Never put essential CTA copy or prices inside images; use HTML text with VML buttons for Outlook compatibility.
Background colors on table cells are a reliable visual fallback for layout areas that rely on images.
Test blocked-image rendering in Outlook and Thunderbird before every campaign send.

Production fallback layer

Use fallback.pics anywhere an image URL is accepted.

Start with one deterministic URL and standardize fallback behavior across your design system.

Read the docs