Classic vs New Outlook: What the 2024–2026 Rendering Change Means for Your Emails
Is Outlook still the email client that uses Microsoft Word to render HTML?
Only the classic version. Classic Outlook for Windows (2007–2021) still renders through the Microsoft Word engine, but the new Outlook for Windows — rolling out since 2024 — uses Microsoft Edge WebView2 (Chromium) and renders like a modern browser. Microsoft plans to retire the Word-based client around October 2026. Until then both engines are live, so you must keep coding for the Word engine while the new Outlook quietly renders the richer version.
If you have ever built an HTML email, you have heard the warning: Outlook renders with Microsoft Word, so half of modern CSS simply does not work. It was the single most important fact in email development. But Outlook has quietly split into two completely different applications with two completely different rendering engines — and the advice that was true for a decade is now only half right.
This is not a general "why emails break" post — for that, see Gmail vs Outlook rendering differences or our HTML email best practices. This is specifically about the Outlook engine change and what it means for your code through 2026.
Meet the two Outlooks
There are now two separate desktop apps that both call themselves "Outlook," and your subscribers are using both at the same time.
Classic Outlook for Windows— the 2007, 2010, 2013, 2016, 2019, and 2021 desktop versions, plus "classic" Microsoft 365 Outlook — renders HTML with the Microsoft Word engine. Word was built for documents, not web layout, which is the source of every Outlook quirk you have fought with.
The new Outlook for Windows — Microsoft began rolling this out in 2024 as the eventual replacement. It is built on the Outlook web experience and renders with Microsoft Edge WebView2, a Chromium engine. In other words, the new Outlook renders email much like Chrome does.
What the Word engine has always broken
Classic Outlook's Word engine does not support flexbox, grid, CSS background-image, or max-width, and it ignores margin and padding on div and imgelements (padding on table cells still works, which is why table layouts survive). Background images are only possible through Microsoft's own VML markup, and web fonts fall back to Times New Roman unless you supply mso-font-alt. If you want the deep workarounds — MSO conditional comments, VML, ghost tables — we cover them in how to test email rendering in Outlook.
What the new Chromium Outlook fixes
Because the new Outlook runs on WebView2, most of the classic limitations disappear. Features that the Word engine silently dropped now render close to how a browser handles them:
- CSS background-image works without a VML fallback.
- border-radius renders real rounded corners instead of squares.
- max-width and modern layout properties are respected.
- Gradients and animated GIFs display properly.
- Web fonts load instead of collapsing to Times New Roman.
It is genuinely good news — but it creates a new problem, because the two engines now live side by side.
The catch: both engines are live at once
Microsoft plans to end support for the classic Word-engine desktop client around October 2026, migrating users to the new Outlook. But "planned end of support" is not the same as "everyone has switched." Organizations delay upgrades, classic Outlook remains installed on millions of machines, and your audience will contain both engines for a long time.
That means you cannot design only for the new Chromium Outlook yet. If you do, your rounded buttons become squares and your background heroes vanish for every subscriber still on classic Outlook. The safe approach is unchanged: code for the Word engine as your floor, and let the new Outlook render the richer version on top.
| Feature | Classic Outlook (Word engine, 2007–2021) | New Outlook (Edge WebView2, 2024+) |
|---|---|---|
| Rendering engine | Microsoft Word | Microsoft Edge WebView2 (Chromium) |
| CSS background-image | No (needs VML) | Yes |
| border-radius | No | Yes |
| max-width | No | Yes |
| Flexbox / grid | No | Yes |
| Padding on div / img | Ignored (use td) | Supported |
| Web fonts | Falls back to Times New Roman | Loads the font |
| Status | Support ending ~Oct 2026 | Rolling out as the default |
How to code for the transition
Until classic Outlook is genuinely gone from your audience, keep these defensive techniques in place — they are invisible to the new Outlook and essential for the old one:
- Keep nested-table layouts for structure rather than flexbox or floated divs.
- Put padding on table cells (
td), not on divs or images. - Wrap background images in a VML fallback so classic Outlook still shows them.
- Add
mso-font-altto your@font-facerules and end every font stack with a web-safe family. - Use MSO conditional comments to feed classic Outlook ghost tables and spacing it can understand.
The payoff: the same email degrades gracefully in the Word engine and renders beautifully in the new Chromium one — no separate version required.
Test both Outlooks before you send
You do not need two Windows machines to verify this. With MailViewr you can paste or upload your HTML — no signup required — and preview an Outlook rendering across desktop and mobile while it flags the CSS that classic Outlook strips, using the same Can I Email compatibility data the email-dev community relies on. That lets you confirm your VML fallbacks, table structure, and font stacks hold up for the Word engine before a single subscriber opens it.
Preview your email for Outlook free
Paste your HTML, preview it across Outlook, Gmail, and Apple Mail on desktop and mobile, and see which CSS classic Outlook strips — no signup required to get started.
Open MailViewr free →