Why email HTML testing is essential
Email clients are not web browsers. Outlook uses the Word rendering engine. Gmail strips <style> tags. Yahoo ignores media queries. What looks perfect in your browser will break in at least one major email client.
MailHog parses your email's HTML and checks every element and CSS property against a compatibility database for 12+ email clients, giving you a per-client report of what will render and what won't.
Clients we check against
CSS properties that break in email clients
These are the most common issues MailHog catches:
- Flexbox / Grid — Not supported in Outlook (uses Word engine)
- CSS animations — Stripped by Gmail, Yahoo, and most clients
- Background images — Partial support; Outlook needs VML fallback
- Media queries — Stripped by Gmail, Yahoo; works in Apple Mail
- Web fonts — Only Apple Mail and Thunderbird support them
- Position/float — Inconsistent across all clients
- SVG — Not supported in Outlook; partial elsewhere
How to use the compatibility report
For every captured email, MailHog's HTML Check tab shows a grid of clients with pass/fail indicators for each CSS property and HTML element used in your email. Click any failing check to see what's unsupported and the recommended workaround.
The most practical approach: design emails with table-based layouts (yes, still), inline CSS, and test against MailHog after every template change. This catches issues before your users report them.
Test your email HTML now
Free plan includes HTML compatibility checks on every captured email.