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Email Compatibility

Check HTML email code for rendering issues across email clients.

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Paste HTML email code. We'll check for rendering issues across email clients.

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How to Check Email HTML Compatibility

Paste your HTML email code and click Check Compatibility. The analyzer scans for CSS properties, layout patterns, and HTML structures that don't render consistently across email clients. You'll get a list of specific issues with the affected clients, plus a checklist showing which compatibility rules your code passes or fails. Fix the flagged issues before sending to avoid broken layouts in your recipients' inboxes.

Why Email HTML Is Different

Email clients are not web browsers. Outlook uses Microsoft Word's rendering engine, which means no flexbox, no grid, no CSS positioning, and limited CSS property support. Gmail strips all style tags and only keeps inline styles. Yahoo does the same. Apple Mail is the most forgiving, but you can't design for just one client. The result is that email HTML is stuck in a world of table layouts and inline styles — the same techniques the web abandoned fifteen years ago. It's not elegant, but it's what works everywhere.

Common Email Rendering Issues

The most common problems are div-based layouts that collapse in Outlook, style blocks that get stripped by Gmail, images without explicit dimensions that render at wrong sizes, and modern CSS like flexbox or grid that simply doesn't exist in email rendering engines. Background images are another frequent offender — Outlook ignores CSS background-image entirely. Each of these has a table-based, inline-styled workaround that this checker helps you identify.

Why doesn't my email look the same in Outlook? +
Outlook on Windows uses Microsoft Word's HTML rendering engine, not a browser engine. Word doesn't support flexbox, grid, CSS positioning, background images, or many common CSS properties. It also interprets margins, padding, and line heights differently than browsers. The fix is table-based layouts with inline styles and explicit dimensions on everything. Outlook on Mac uses WebKit and renders like a browser, but most Outlook users are on Windows.
Can I use CSS in HTML emails? +
Yes, but only inline styles. Gmail, Yahoo, and many other clients strip style tags from the head and body, so any CSS in a style block won't apply. Put every style directly on the element using the style attribute. Stick to well-supported properties: color, font-family, font-size, font-weight, text-align, padding (longhand), margin (longhand), border, background-color, width, and height. Avoid shorthand properties where possible — some clients parse them incorrectly.
What's the safest HTML structure for emails? +
A centered table with a fixed width (600px is the standard), containing nested tables for each content section. Every element gets inline styles. Images have explicit width and height attributes (not just CSS). Links use inline color and text-decoration styles. No div elements for layout — only for semantic grouping where they don't affect rendering. It looks like HTML from 2003, and that's exactly the point.
How do I test across email clients? +
Start here — this checker catches the most common structural and CSS issues before you send. For visual testing, services like Litmus and Email on Acid render your email across dozens of clients and show you screenshots. For quick manual testing, send test emails to Gmail, Outlook.com, Yahoo Mail, and Apple Mail accounts. The biggest rendering differences are between Gmail (strips styles), Outlook Windows (Word engine), and Apple Mail (permissive). If it looks right in those three, it'll work almost everywhere.
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