Why Outlook still matters
Ah, Outlook. Known for inducing a collective sigh and shrug from any email designer or anyone in the industry. It’s a pain in the butt to design for (we’ll get into why), and breaks even when every other test doesn’t seem to. Why? And more importantly, what can be done to avoid this headache? We’ll dig into this.
Outlook may feel like a small issue with a low number of email recipients overall, but it can still be a big topic for your list. Litmus’s July 2026 data puts Outlook at 5.83% of tracked opens, behind Apple (62.26%) and Gmail (27.03%). And the trouble is, that even if it’s an objectively small percentage of email recipients globally, that doesn’t mean it’s negligible. Those few with Outlook may have a disproportionally large voice in email design! (Think of the common use case where management level roles use Outlook even when typical customers may not).
Depending on your industry, that overall average can be misleading. Corporate inboxes tend to still run on Microsoft 365, and Outlook isn’t an outlier here, you need to design for it.
This post covers why Outlook behaves differently, the issues you’ll hit most, the design rules that hold up, and how to test before you send.
Why Outlook is different: there isn’t one Outlook
“Outlook” is really a family of apps, and they don’t share a rendering engine. Classic Outlook on Windows (2007 through 2019, plus the Microsoft 365 desktop app) renders HTML with Microsoft Word, rather than with a web browser. That’s the root of nearly every Outlook headache.
| Outlook version | Rendering engine | How hard to design for |
|---|---|---|
| Classic Outlook for Windows (2007 to 2019, Microsoft 365 desktop) | Microsoft Word | Hard: needs tables, VML and conditional code |
| New Outlook for Windows | Web browser engine | Much easier, closer to Outlook.com |
| Outlook for Mac | WebKit | Easy, similar to Apple Mail |
| Outlook.com and Outlook on the web | WebKit or Blink | Easy |
| Outlook for iOS and Android | WebKit-based | Easy |
Microsoft is moving Windows users to the new Outlook, but the switch is gradual. Check your specific ESP’s client report: as long as classic Outlook shows up for your audience, you have to design for the Word engine. (Sorry, but it’s true.)
Top Pitfalls
These are the most common issues you’ll run into when designing for classic Outlook on Windows, why they happen, and how to avoid them.
- Broken layouts and columns: Outlook doesn’t support modern CSS layouts like flexbox and grid. Build your email structure with HTML tables instead.
- Oversized or distorted images: Outlook can ignore CSS image sizing, especially with Windows DPI scaling. Set explicit width and height attributes on every image.
- Missing padding and margins: Spacing applied to images or divs may not render as expected. Use padding on table cells (td) for more reliable spacing.
- Scaling issues on high-resolution screens: Windows DPI settings can make email elements appear larger than intended. Add the Office XML namespace and PixelsPerInch setting to help prevent unwanted scaling.
- Square buttons and missing backgrounds: Classic Outlook doesn’t support border-radius or CSS background images reliably. Use VML for rounded buttons and background images, with solid-color fallbacks.
- Blocked images: Some Outlook configurations block images by default, leaving empty spaces in your email. Include descriptive ALT text and keep important messaging in live text.
- Frozen animated GIFs: Classic Outlook typically displays only the first frame of an animated GIF. Make sure that frame communicates the message on its own.
Sources: Litmus, Can I Email: Outlook, Can I Email: border-radius
Design considerations that hold up in Outlook
The goal isn’t pixel-perfect sameness everywhere. It’s an email that works in Outlook and also shows up great everywhere else.
Design rules
- Keep the layout simple. A single column, or two columns at most, survives the Word engine far better than complex grids.
- Use a fixed width around 600px with tables, so Outlook doesn’t stretch the email across a wide reading pane.
- Put key messages as text, not only in images. With image blocking a common issue, a text headline and a real button get the point across safely.
- Choose web-safe fallback fonts. Custom web fonts don’t reliably load in classic Outlook, so pick a fallback (Arial, Georgia, Segoe UI) you’re happy to see.
- Keep the design simple. Rounded corners, gradients and hover states may look great, but Outlook won’t display those kinds of extras. If you can get a clean, simple design that works for everyone, you’ll have a simpler time QAing emails.
For further reading: For more technical guidance on Outlook-specific code, including conditional comments, DPI fixes, and VML, check out Good Email Code and Can I Email.
Why testing matters, and which tools to use in 2026
Most people can’t design for Outlook from memory alone. The same email can look perfect in Outlook for Mac and broken in classic Outlook on Windows, and you won’t know unless you look. Test every new template, and every campaign with layout changes.
The testing market has shifted a lot this year. Litmus is now part of Validity Engage, and Email on Acid customers are moving to Mailgun Inspect.
The short version for Outlook testing:
- Check before you build: Can I Email shows feature support for each Outlook version, for free.
- Preview across versions: Use a rendering tool that supports classic Outlook for Windows.
- Test in a real inbox: Keep a Windows machine or virtual machine with classic Outlook, and a seed account in the new Outlook. Screenshots don’t show you how the email scrolls or behaves in dark mode.
- Test with images off: Confirm the email still makes sense with ALT text only.
What to do before your next send
How much you should worry about—and design for—Outlook depends on your specific list and audience. So before you redesign and test every email, start by checking your email platform’s reporting to see which email clients and devices your subscribers use. Not every platform provides this breakdown easily, but many do. It’s a great way to identify where to focus your testing efforts and get buy-in for the extra time spent.
Tip: If you’re not sure how to see this in your email platform, ask their helpdesk for guidance. “I’m trying to understand our subscribers’ email clients and devices. How can I find this information in our account?”
And remember, Outlook is just one piece of the email puzzle. There’s plenty more to check before hitting send. For a broader look at email QA, take a look at our 20 Questions to Ask When Scheduling an Email Campaign.
Need a hand?
Email rendering can be frustrating, especially when everything looks perfect in one inbox and completely different in another.
At Centric Squared, we design, build, and test emails across different clients and devices, so you don’t have to troubleshoot every rendering issue yourself.
Have questions or need an extra set of eyes on your emails? Book a discovery call, we’d love to help.