Outlook 2010 and the Word Rendering Engine: The Inevitable Letdown

Outlook 2010 shipped in 2010 still rendering HTML email with Microsoft Word, and every classic Outlook for Windows since then has done the same, including Outlook 2013, 2016, 2019, 2021, 2024 and classic Outlook in Microsoft 365. The big change is the new Outlook for Windows. It drops Word and renders mail with Microsoft Edge WebView2 (Chromium), so modern CSS such as background images and media queries works there. Classic Outlook is supported until at least 2029, though, so in November 2026 you still have to build emails that hold up in the Word engine.

Apparently the fixoutlook.org campaign was “too little, too late.” By the time the campaign hit its stride in June 2009 and Microsoft took notice, the company had already started building the next version of its desktop client, Outlook 2010. The new client kept the one thing email marketers found hardest to live with: it used the Word engine to display their emails.

Dave Greiner from CampaignMonitor did a lot to put the problem on Microsoft’s radar in the first place. Campaign Monitor co-founded the Email Standards Project, the group behind the campaign, and Greiner had been writing to Microsoft’s development team directly for some time. He reported the following from them:

“At this point, our plans for email authoring and rendering in Outlook 2010 are unchanged. However, I can tell you that this is a significant topic of discussion as we plan our business going forward, and something we will definitely be thinking about for future releases of Outlook.”

Microsoft also answered in public. Corporate vice president William Kennedy confirmed that Outlook 2010 would use Word 2010 to compose and display email, as Office 2007 did. He argued that the industry had no agreed standard for which HTML subset email should support, and that the Email Standards Project was not a recognised standards body.

Litmus, the well-known email testing service, had access to the Outlook 2010 beta and posted their results here. The results were no surprise. They matched what designers already knew from Outlook 2007: tables for layout, weak CSS support, and no background images without workarounds.

The post ended in hope: “So hopefully by 2013, Microsoft will release another email client, this time with a much better rendering engine, so that elements such as background images render correctly. Emphasis on ‘hopefully’.” That hope did not come true in 2013. Outlook 2013 kept the Word engine, and so did every classic desktop version after it.

What happened after Outlook 2010

The Word engine lasted more than a decade after the campaign, and Microsoft only left it behind with a separate app. In practice, each new classic version brought small fixes (better high-DPI scaling, for example) but the same core limits on CSS.

The versions that frustrated designers in 2009 and 2010 are now history:

• Outlook 2007 brought in the Word engine in the first place. It is long out of support.
• Outlook 2010 reached end of support on October 13, 2020.
• Outlook 2013 reached end of support on April 11, 2023.
• Outlook 2016 and 2019 reached end of support on October 14, 2025, together with the rest of Office 2016 and 2019. They no longer get security updates.
• Office 2021 and Office LTSC 2021 reached end of support on October 13, 2026.

Unsupported does not mean gone. Some offices still run these versions, which is one reason Word-engine fallbacks are still worth keeping.

How Outlook renders email in November 2026

There are now two families of Outlook on Windows, and they render the same email very differently. Classic Outlook uses Word. The new Outlook for Windows uses the same web engine as Outlook on the web.

The new Outlook timeline

Microsoft planned to make the new Outlook the default for Microsoft 365 Apps for enterprise users in April 2026, then moved that “opt-out” phase to March 2027. After the final “cutover” phase, organisations with the right licences can still download classic Outlook separately. Microsoft says existing classic installations stay supported until at least 2029. Treat that as the earliest date, not a fixed end date.

What that means for your templates

Code for classic Outlook as your baseline and let the newer clients show the richer version. Business audiences keep the Word engine in their mix longer than consumer lists do, because many firms rely on classic-only features such as COM add-ins and VBA macros.

1. Keep table-based layout or a hybrid layout with Outlook conditional comments (<!, [if mso]>).
2. Use VML for background images in classic Outlook, with a solid background colour as a fallback.
3. Set widths in HTML attributes as well as CSS, because Word ignores many CSS properties.
4. Test in classic Outlook, the new Outlook and Outlook.com separately in a service such as Litmus or Email on Acid.
5. Check dark mode. Outlook clients can partly or fully invert colours, so transparent logos and dark text on transparent backgrounds can vanish.

Why Outlook matters less (and more) than it used to

Litmus’s 2026 email client market share data puts Apple Mail and Gmail far ahead, with Outlook desktop in the single digits of tracked opens. That figure undercounts Outlook’s real importance for B2B senders. Apple Mail Privacy Protection preloads images, which inflates Apple’s open counts. Gmail’s image proxy also hides some client detail. Look at your own list’s client report before you decide how much effort the Word engine deserves.

Rendering is no longer the only Outlook hurdle

Getting into the inbox now matters as much as how the email looks once it arrives. Gmail and Yahoo brought in bulk sender rules in February 2024. They require SPF, DKIM and DMARC, one-click unsubscribe, and a spam complaint rate below 0.3%, and Google recommends staying under 0.1%. Gmail stepped up enforcement in November 2025. Microsoft added similar rules for Outlook.com, Hotmail.com and Live.com from May 5, 2025, for senders of more than 5,000 messages a day. Failing mail can be rejected with a 550 5.7.15 error.

A minimal DMARC record that meets the baseline looks like this:

_dmarc.example.com. TXT "v=DMARC1; p=none; rua=mailto:[email protected]"

A beautifully coded email still goes nowhere if your sending domain fails authentication. So fix your DNS before you spend time on VML.

FAQ

Does Outlook still use Word to render HTML emails?

Classic Outlook for Windows does, in every version from Outlook 2007 through Outlook 2024 and classic Outlook in Microsoft 365. The new Outlook for Windows does not. It uses Edge WebView2, the Chromium engine behind Outlook on the web. If your list includes readers on both, design for each.

When will classic Outlook go away?

Microsoft says support for existing installations of classic Outlook for Windows will continue until at least 2029, though the exact support period depends on the Office version and its lifecycle. The step that makes the new Outlook the default for enterprise users moved from April 2026 to March 2027. Even after that, licensed organisations can install classic Outlook separately, so expect Word-engine rendering in business inboxes for years to come.

Do background images work in Outlook now?

They work in the new Outlook for Windows and in Outlook.com, because both use a modern web engine. Classic Outlook still needs VML markup inside conditional comments to show a background image. Always set a solid background colour as the fallback.

Is it still worth supporting Outlook 2010 or 2013?

Microsoft no longer supports either version. Outlook 2010’s support ended in 2020 and Outlook 2013’s in 2023. They use the same Word engine as current classic Outlook, though, so an email that works in Outlook 2024 or Microsoft 365 usually works in them too. Spending separate effort on them only makes sense if your own client reports show real opens.

Why does my email look fine in Outlook.com but broken in Outlook desktop?

Outlook.com renders in your browser, while classic desktop Outlook renders with Word. Word ignores CSS such as floats, flexbox, many margin and padding rules on some elements, and most background images. Fix it with table layouts, HTML width attributes and Outlook-only conditional code.

Sources

• Microsoft 365 Blog: Office 2016 and 2019 have reached end of support
• Microsoft Learn: New Outlook for Windows rollout and classic Outlook support timeline
• Microsoft Tech Community: Outlook’s new requirements for high-volume senders (April 2025)
• Google Workspace Admin Help: Email sender guidelines and FAQ
• Yahoo Sender Hub: Sender requirements and best practices
• Litmus: Email client market share and Outlook rendering guide
• Mailjet Help Center: Outlook rendering issues
• FTC: CAN-SPAM Act compliance guide for business