Superhuman
Superhuman uses the Blink rendering engine (the same engine as Chrome), giving it excellent CSS support. It renders most modern CSS properties correctly, including flexbox, custom fonts, and CSS animations. It's one of the most capable email clients from a rendering perspective.
A premium email client ($30/month) popular among executives, investors, and productivity-focused professionals. Small market share but high-value audience , common in VC, finance, and tech leadership.
CSS coverage profile for Superhuman
Superhuman renders with the Blink engine and supports 84 of 298 tracked CSS and HTML features fully, with 5 partially supported and 6 unsupported. That places it in a narrow coverage band.
Most modern CSS is unsupported. This client effectively requires a separate, table-based fallback path for any non-trivial layout.
84
Supported
5
Partial
6
Unsupported
298
Total
Key gotchas in Superhuman
Interactive elements While Superhuman renders interactive CSS and HTML well, email interaction doesn't persist. Don't rely on :checked or form state.
Image loading Superhuman may proxy or cache images. Use absolute URLs for all image sources and don't rely on server-side image tracking.
How Superhuman renders email
- Built on Blink (Chromium), so Superhuman effectively renders email like a modern browser. Flexbox, grid, custom properties, and modern selectors (:has, :is) work as expected.
- Image proxy and caching are aggressive. Images are fetched server-side, stripped of tracking parameters, and re-served from Superhuman's infrastructure. Open-tracking pixels and per-recipient image hashing fail.
- @font-face is supported, but Superhuman's read-mode UI applies its own typography hierarchy on top of the email content, which can interact unexpectedly with custom font sizing.
- Dark mode is theme-driven , Superhuman has its own theming system that overlays user-side styles regardless of color-scheme meta tags. Test dark mode visuals from inside the Superhuman client, not just via prefers-color-scheme simulation.
Dark mode behaviour in Superhuman
Superhuman has a built-in dark mode theme that applies intelligent color inversion. It uses Blink's rendering capabilities to handle dark mode well, but custom color schemes should still be tested explicitly.
QA checklist for Superhuman
- Verify image rendering in Superhuman directly , the proxying behaviour can subtly alter quality and remove tracking-dependent visuals.
- Avoid embedding tracking pixels for Superhuman audiences , they will be stripped or proxied, distorting open metrics.
- Check link previews: Superhuman shows preview cards for some URLs that override your in-email layout decisions.
Renders here, dropped almost everywhere else
Safe in Superhuman and almost nowhere else, so it needs a fallback the moment the send is not Superhuman-only.
Where Superhuman is weakest
- CSS Properties 5
- HTML Elements 4
- CSS At-Rules 2
Closest client: HEY Mail
HEY Mail agrees with Superhuman on 91% of verified features. They still differ on 7: <picture>, <svg>, @import, @keyframes, animation, transform, and 1 more.
Side by side
HTML Elements48
| Feature | Support |
|---|---|
| <abbr> | Unknown |
| <acronym> | Unknown |
| <address> | Unknown |
| <audio> | Unsupported |
| <base> | Unknown |
| <bdi> | Unknown |
| <blockquote> | Unknown |
| <body> | Unknown |
| <button type="reset"> | Unknown |
| <button type="submit"> | Unknown |
| <code> | Unknown |
| <del> | Unknown |
| <dfn> | Unknown |
| <dialog> | Unknown |
| <div> | Unknown |
| <form> | Unsupported |
| <h1> | Unknown |
| <hr> | Unknown |
| <img> | Unknown |
| <input type="checkbox"> | Unknown |
| <input type="hidden"> | Unknown |
| <input type="radio"> | Unknown |
| <input type="reset"> | Unknown |
| <input type="submit"> | Unknown |
| <input type="text"> | Unknown |
| <link> | Unsupported |
| <marquee> | Unknown |
| <meter> | Unknown |
| <object> | Unknown |
| <p> | Unknown |
| <picture> | Supported |
| <pre> | Unknown |
| <progress> | Unknown |
| <rp> | Unknown |
| <rt> | Unknown |
| <ruby> | Unknown |
| <select> | Unknown |
| <small> | Unknown |
| <span> | Unknown |
| <strike> | Unknown |
| <strong> | Unknown |
| <style> | Supported |
| <svg> | Supported |
| <table> | Unknown |
| <textarea> | Unknown |
| <ul> | Unknown |
| <video> | Unsupported |
| <wbr> | Unknown |
HTML Attributes22
| Feature | Support |
|---|---|
| [align] | Unknown |
| [aria-describedby] | Unknown |
| [aria-hidden] | Unknown |
| [aria-label] | Unknown |
| [aria-labelledby] | Unknown |
| [aria-live] | Unknown |
| [background] | Unknown |
| [cellpadding] | Unknown |
| [cellspacing] | Unknown |
| [command] | Unknown |
| [dir] | Unknown |
| [height] | Unknown |
| [hidden] | Unknown |
| [lang] | Unknown |
| [loading] | Unknown |
| [popover] | Unknown |
| [required] | Unknown |
| [role] | Unknown |
| [srcset] | Unknown |
| [target] | Unknown |
| [valign] | Unknown |
| [width] | Unknown |
HTML & Email Structure8
| Feature | Support |
|---|---|
| amp4email | Unknown |
| anchor-links | Unknown |
| doctype | Unknown |
| html-comments | Unknown |
| html5-semantics | Unknown |
| image-maps | Unknown |
| mailto-links | Unknown |
| meta-color-scheme | Unknown |
CSS At-Rules10
| Feature | Support |
|---|---|
| @font-face | Supported |
| @import | Unsupported |
| @keyframes | Partial |
| @media | Supported |
| @media device-pixel-ratio | Unknown |
| @media hover | Unknown |
| @media orientation | Unknown |
| @media prefers-color-scheme | Unknown |
| @media prefers-reduced-motion | Unknown |
| @supports | Supported |
Pseudo-Elements6
| Feature | Support |
|---|---|
| ::after | Unknown |
| ::before | Unknown |
| ::first-letter | Unknown |
| ::first-line | Unknown |
| ::marker | Unknown |
| ::placeholder | Unknown |
Pseudo-Classes & Selectors34
| Feature | Support |
|---|---|
| :adjacent-sibling | Unknown |
| :attribute-selector | Unknown |
| :chaining | Unknown |
| :checked | Unknown |
| :child-combinator | Unknown |
| :class-selector | Unknown |
| :descendant-combinator | Unknown |
| :first-child | Unknown |
| :first-of-type | Unknown |
| :focus | Unknown |
| :focus-visible | Unknown |
| :focus-within | Unknown |
| :general-sibling | Unknown |
| :grouping | Unknown |
| :has | Unknown |
| :hover | Unknown |
| :id-selector | Unknown |
| :lang | Unknown |
| :last-child | Unknown |
| :last-of-type | Unknown |
| :link | Unknown |
| :not | Unknown |
| :nth-child | Unknown |
| :nth-last-child | Unknown |
| :nth-of-type | Unknown |
| :only-child | Unknown |
| :only-of-type | Unknown |
| :target | Unknown |
| :type-selector | Unknown |
| :universal-selector | Unknown |
| :visited | Unknown |
| pseudo-class-active | Unknown |
| pseudo-class-default | Unknown |
| pseudo-class-nth-last-of-type | Unknown |
CSS Functions8
| Feature | Support |
|---|---|
| calc | Unknown |
| clamp | Unknown |
| conic-gradient | Unknown |
| fit-content | Unknown |
| linear-gradient | Supported |
| max | Unknown |
| min | Unknown |
| radial-gradient | Supported |
CSS Properties162
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Support data last updated Sep 2, 2026 - synced from caniemail.com (MIT) via @emailens/engine.