HEY Mail
HEY Mail is built by Basecamp and uses a WebKit-based rendering engine. It has good overall CSS support but takes an opinionated approach to email display , it strips tracking pixels, modifies some layout properties, and applies its own reading experience on top of your HTML.
A niche but growing email client from Basecamp, popular among tech professionals and early adopters. Small market share but influential in the developer community.
CSS coverage profile for HEY Mail
HEY Mail renders with the WebKit engine and supports 171 of 298 tracked CSS and HTML features fully, with 10 partially supported and 53 unsupported. That places it in a moderate coverage band.
A meaningful portion of CSS is unsupported or partially supported. Plan fallbacks for layout-critical features and validate every template before send.
171
Supported
10
Partial
53
Unsupported
298
Total
Key gotchas in HEY Mail
Tracking pixels HEY aggressively blocks tracking pixels and remote image loading by default. Open-rate tracking won't work for HEY users.
Layout modifications HEY may modify your email's width and padding to fit its reading experience. Fixed-width layouts can break.
External fonts External font loading may be blocked as part of HEY's privacy-first approach. Rely on system font stacks.
How HEY Mail renders email
- HEY's reading experience overlay applies its own typography hierarchy and spacing on top of the email content. Designs that depend on precise edge-to-edge spacing should account for HEY's wrapper padding.
- Tracking pixel detection is aggressive , known tracking domains and 1×1 transparent images are stripped or replaced. Open-rate analytics that depend on these mechanisms will under-count HEY users.
- External @font-face fetches may be blocked under HEY's privacy-first defaults. Always supply a complete system-font fallback stack rather than relying on a single custom font.
- Image loading is opt-in for unknown senders, so first-open rendering shows alt text and image placeholder boxes. Design with explicit width/height attributes so layout doesn't reflow when images load.
Dark mode behaviour in HEY Mail
HEY supports dark mode through its app theme. It applies its own styling adjustments in dark mode. Because HEY modifies the email display layer, your dark mode CSS may not apply as expected.
QA checklist for HEY Mail
- Validate that the email reads cleanly without external resources , HEY's privacy stance often blocks them on first open.
- Test the alt-text and placeholder rendering , HEY users see this state more often than users of less-privacy-strict clients.
- Avoid embedding tracking pixels for HEY audiences; they will be stripped, and any analytics depending on them will under-report.
Breaks here, works nearly everywhere else
15 features that HEY Mail drops while most other clients render them. This is usually what is behind an email that looks correct everywhere but here.
Renders here, dropped almost everywhere else
Safe in HEY Mail and almost nowhere else, so it needs a fallback the moment the send is not HEY Mail-only.
Where HEY Mail is weakest
- HTML Elements 31
- HTML Attributes 16
- HTML & Email Structure 6
- CSS Properties 6
- Pseudo-Classes & Selectors 2
Closest client: Superhuman
Superhuman agrees with HEY Mail 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> | Unsupported |
| <acronym> | Unknown |
| <address> | Supported |
| <audio> | Unsupported |
| <base> | Partial |
| <bdi> | Unsupported |
| <blockquote> | Partial |
| <body> | Partial |
| <button type="reset"> | Unsupported |
| <button type="submit"> | Unsupported |
| <code> | Supported |
| <del> | Supported |
| <dfn> | Unknown |
| <dialog> | Unsupported |
| <div> | Supported |
| <form> | Unsupported |
| <h1> | Supported |
| <hr> | Unknown |
| <img> | Supported |
| <input type="checkbox"> | Unsupported |
| <input type="hidden"> | Unsupported |
| <input type="radio"> | Unsupported |
| <input type="reset"> | Unsupported |
| <input type="submit"> | Unsupported |
| <input type="text"> | Unsupported |
| <link> | Unsupported |
| <marquee> | Unsupported |
| <meter> | Unsupported |
| <object> | Unsupported |
| <p> | Supported |
| <picture> | Unsupported |
| <pre> | Supported |
| <progress> | Unsupported |
| <rp> | Unsupported |
| <rt> | Unsupported |
| <ruby> | Unsupported |
| <select> | Unsupported |
| <small> | Supported |
| <span> | Supported |
| <strike> | Unsupported |
| <strong> | Supported |
| <style> | Supported |
| <svg> | Unsupported |
| <table> | Supported |
| <textarea> | Unsupported |
| <ul> | Supported |
| <video> | Unsupported |
| <wbr> | Unsupported |
HTML Attributes22
| Feature | Support |
|---|---|
| [align] | Partial |
| [aria-describedby] | Unsupported |
| [aria-hidden] | Unsupported |
| [aria-label] | Unsupported |
| [aria-labelledby] | Unsupported |
| [aria-live] | Unsupported |
| [background] | Unsupported |
| [cellpadding] | Unknown |
| [cellspacing] | Unknown |
| [command] | Unknown |
| [dir] | Supported |
| [height] | Unsupported |
| [hidden] | Unknown |
| [lang] | Unsupported |
| [loading] | Partial |
| [popover] | Unsupported |
| [required] | Unsupported |
| [role] | Unsupported |
| [srcset] | Unsupported |
| [target] | Unsupported |
| [valign] | Supported |
| [width] | Unsupported |
HTML & Email Structure8
| Feature | Support |
|---|---|
| amp4email | Unsupported |
| anchor-links | Unsupported |
| doctype | Unsupported |
| html-comments | Unknown |
| html5-semantics | Partial |
| image-maps | Unsupported |
| mailto-links | Supported |
| meta-color-scheme | Unsupported |
CSS At-Rules10
| Feature | Support |
|---|---|
| @font-face | Supported |
| @import | Supported |
| @keyframes | Supported |
| @media | Supported |
| @media device-pixel-ratio | Supported |
| @media hover | Unknown |
| @media orientation | Supported |
| @media prefers-color-scheme | Unsupported |
| @media prefers-reduced-motion | Supported |
| @supports | Supported |
Pseudo-Elements6
| Feature | Support |
|---|---|
| ::after | Supported |
| ::before | Supported |
| ::first-letter | Supported |
| ::first-line | Supported |
| ::marker | Supported |
| ::placeholder | Unsupported |
Pseudo-Classes & Selectors34
| Feature | Support |
|---|---|
| :adjacent-sibling | Supported |
| :attribute-selector | Supported |
| :chaining | Supported |
| :checked | Unsupported |
| :child-combinator | Supported |
| :class-selector | Supported |
| :descendant-combinator | Supported |
| :first-child | Supported |
| :first-of-type | Supported |
| :focus | Supported |
| :focus-visible | Unknown |
| :focus-within | Unknown |
| :general-sibling | Supported |
| :grouping | Supported |
| :has | Supported |
| :hover | Supported |
| :id-selector | Supported |
| :lang | Unknown |
| :last-child | Supported |
| :last-of-type | Supported |
| :link | Supported |
| :not | Supported |
| :nth-child | Supported |
| :nth-last-child | Supported |
| :nth-of-type | Supported |
| :only-child | Supported |
| :only-of-type | Supported |
| :target | Unsupported |
| :type-selector | Supported |
| :universal-selector | Supported |
| :visited | Supported |
| pseudo-class-active | Supported |
| pseudo-class-default | Unknown |
| pseudo-class-nth-last-of-type | Supported |
CSS Functions8
| Feature | Support |
|---|---|
| calc | Supported |
| clamp | Supported |
| conic-gradient | Supported |
| fit-content | Supported |
| linear-gradient | Supported |
| max | Supported |
| min | Supported |
| radial-gradient | Supported |
CSS Properties162
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Support data last updated Sep 2, 2026 - synced from caniemail.com (MIT) via @emailens/engine.