You’ve spent hours on a campaign. Design approved. Team signs off. You hit send.
Ten minutes later, someone forwards a screenshot from their Outlook inbox. Broken layout. Oversized images. A two-column block now stacked vertically.
If this sounds familiar, you’re not alone – and it’s not your team’s fault.
The Root Cause
Most email clients like Gmail, Apple Mail, Yahoo render HTML using a browser engine. CSS works the way you’d expect.
Outlook doesn’t do this.
Desktop Outlook (2007 through Microsoft 365) uses the Microsoft Word rendering engine. Word was built for documents, not web pages. It ignores many standard CSS properties and handles layout in its own way.
That one fact explains almost every Outlook rendering issue.
The 5 Most Common Breaks
1. Images at the wrong size Outlook ignores CSS dimensions on images. Retina images (exported at 2x) display at full file size – blowing out the entire layout. (Litmus)
2. Columns that collapse Outlook doesn’t support flexbox or grid. Your two-column section becomes a vertical list. The only reliable fix is table-based layout – something most modern design tools don’t output. (Email on Acid)
3. Phantom gaps between blocks Random grey or white lines between sections. The cause is always structural – Outlook adds its own default spacing that other clients don’t. (Litmus)
4. Background images gone CSS background-image simply doesn’t work in Outlook. Getting it right requires VML – a Microsoft-specific markup language almost no one writes by hand. Without it, your branded backgrounds become flat blocks of colour. (Email on Acid)
5. Wrong fonts Web fonts (Google Fonts, Adobe Fonts) don’t load in Outlook. It falls back to system fonts – which may not match your brand. Copy spacing also shifts because Outlook applies its own line-height rules. (Email on Acid)
It’s Not One Outlook — It’s Many
Testing in “Outlook” isn’t enough. There are four desktop versions (2016, 2019, 2021, 365), each rendering slightly differently. Outlook on Mac uses WebKit – closer to a browser. Outlook on the web is different again.
When your team sends a test to “their Outlook,” they’re testing one version on one machine. That’s not the same as knowing your email holds up across all of them.
What Actually Helps
- Test against a full rendering matrix – tools like Email on Acid or Litmus show your email across 40+ clients before it goes out
- Start with Outlook-compatible templates – structural decisions at the code level can’t be fixed later with CSS patches
- Don’t trust design-to-code exports – most generate browser-ready HTML, not Outlook-ready HTML
The honest reality: options 2 and 3 require either a specialist developer, or templates that have already solved this before your team touches them.
The Real Fix Is Upstream
Outlook rendering issues are a symptom. The root problem is templates that weren’t built with the full client matrix in mind from day one.
Teams that stop debugging Outlook aren’t better resourced – they’re building on a foundation that handles it before campaigns even reach their hands.
If your team is still spending time on this, it’s worth a conversation.
At Cirro, we help SFMC teams solve exactly this — through custom email template builds designed for cross-client rendering from the ground up. If your team is tired of debugging Outlook on every campaign, let’s talk.
