Email client support
Email clients do not follow a single rendering standard. Apple Mail uses WebKit, Gmail runs Blink in a sandbox, and Outlook for Windows still uses the Microsoft Word engine. Many smaller clients add their own quirks on top. This means identical HTML can display differently depending on the platform. Rigorous cross-client testing is the only reliable way to detect these inconsistencies before emails are sent.
Test coverage based on real data
Litmus analytics from April 2025, based on 1.3 billion real opens, show the following client shares: Apple Mail ≈ 49%, Gmail ≈ 28%, and Outlook variants ≈ 8%. These three account for over 85% of email traffic.
Our release process replicates this client mix using the Litmus preview suite. Each email template is tested in over 100 real combinations of operating system, browser shell and dark-mode setting. The goal is to establish a high-confidence baseline in dominant clients. Teams can expand the testing matrix based on their own analytics.
Outlook for Windows: handled by fallback structures
Outlook for Windows renders HTML using the Microsoft Word engine, which does not support many modern CSS features. To manage this, the framework defaults to:
table-based layouts
inline styles
PNG/SVG alternatives
These fallbacks preserve layout, spacing and iconography under Outlook’s constraints.
Gmail: modern CSS with practical controls
According to Google's May 2025 developer guide, Gmail supports most selectors, attributes and media queries. Maizzle supports this by inlining Tailwind utility classes at build time. This approach ensures styles survive Gmail's sanitation filters and image caching.
Secondary and emerging email clients
For clients like Yahoo Mail, Samsung Email, Proton and Thunderbird, each component is checked against Can I Email support tables. Where support is partial, documentation explains fallback behaviour—often a single-column layout or simplified button. This helps developers assess risk when adopting new patterns.
Ongoing verification
Client rendering engines are updated monthly. Each release triggers the full Litmus suite. A single CLI command lets other teams re-run these previews after customising the codebase. Regression screenshots help identify issues early and maintain alignment with the specification.