Email Client Compatibility

April 1, 2026 · View on GitHub

Inky generates HTML that works across all major email clients. This table shows the rendering engine used by each client and any notable limitations.

Support Matrix

Client	Rendering Engine	Grid	Media Queries	`<style>` Block	Background Images	VML Buttons	Notes
Apple Mail	WebKit	Yes	Yes	Yes	Yes	N/A	Best-in-class rendering
Outlook 2007	Word	Yes	No	Partial	No	Yes	Most restrictive. Use VML for advanced styling.
Outlook 2010	Word	Yes	No	Partial	No	Yes	Same as 2007
Outlook 2013	Word	Yes	No	Partial	No	Yes	Same as 2007
Outlook 2016	Word	Yes	No	Partial	No	Yes	Same as 2007
Outlook 2019	Word	Yes	No	Partial	No	Yes	Same as 2007
Thunderbird	Gecko	Yes	Yes	Yes	Yes	N/A	Generally reliable

Client	Grid	Media Queries	`<style>` Block	Background Images	Notes
Gmail (web)	Yes	Yes	Yes (since 2016)	Yes	Strips unsupported CSS properties. Prefixes class names.
Outlook.com	Yes	Yes	Yes	Yes	Different engine from Outlook desktop. Generally good.
Yahoo Mail	Yes	Yes	Yes	Yes	Good support. Some quirks with `<style>` specificity.
Office 365 (web)	Yes	Yes	Yes	Yes	Similar to Outlook.com
AOL Mail	Yes	Yes	Yes	Yes	Similar to Yahoo Mail (same parent company)
ProtonMail	Yes	No	Partial	Yes	Strips some styles for security. Images blocked by default.
Fastmail	Yes	Yes	Yes	Yes	Good overall support

Client	Grid	Media Queries	`<style>` Block	Notes
iOS Mail	Yes	Yes	Yes	WebKit-based. Excellent rendering.
Gmail app (iOS)	Yes	Yes	Yes	Better support than Android counterpart
Gmail app (Android)	Yes	No	No	Renders large/desktop breakpoint. Does not support media queries.
Outlook app (iOS/Android)	Yes	Yes	Yes	Good rendering, different from Outlook desktop
Samsung Mail	Yes	Yes	Yes	WebKit-based
Yahoo app	Yes	Yes	Yes	Good support

The most restrictive rendering environment. Microsoft Outlook on Windows uses the Word HTML renderer, which means:

No float, position, flexbox, or grid — tables only
No background-image via CSS — use VML or the <hero> component
No border-radius via CSS — Inky uses VML <v:roundrect> for bulletproof buttons
No max-width — use fixed width on tables
No rgba() or hsla() — use solid hex colors
margin is unreliable — use padding on table cells or the <spacer> component
DPI scaling affects images — always set explicit width and height on images
Conditional comments work — <!--[if mso]> lets you target Outlook specifically

Inky handles all of these automatically in its generated output.

The most capable rendering engine for email. Supports:

Gmail has improved significantly since 2016 when it added <style> block support. Current behavior:

Supports <style> blocks in <head>
Prefixes all class names (e.g., .button becomes .m_button) — avoid overly generic names
Strips unsupported CSS properties
Clips emails over 102KB — use inky validate to check
Gmail app on Android still does not support media queries

You don't need to memorize this table. Inky handles cross-client compatibility in its output:

Problem	Inky's Solution
Outlook ignores `<div>` layout	Generates `<table>` markup (or MSO fallbacks in `--hybrid` mode)
Gmail strips `<style>`	Inlines CSS by default
Outlook ignores `border-radius`	VML `<v:roundrect>` bulletproof buttons
Outlook ignores `background-image`	VML background in `<hero>` component
Images blocked by default	Validator flags missing `alt` text
Gmail clips large emails	Validator warns about 102KB threshold
Outlook spacing unreliable	`<spacer>` generates a fixed-height table row
Accessibility	`role="presentation"` on all layout tables

Inky uses a single responsive breakpoint at 596px ($global-breakpoint in SCSS).

This single breakpoint is sufficient for email because:

Rendering varies across clients and changes over time. Always test before sending: