How many CSS features work in every email client?

6 of 298 tracked features are supported in all 21 clients we cover, as of Sep 2, 2026. 173 work somewhere but need a fallback, 91 fail in at least half the field, and 28 have no recorded failures but still carry untested clients.

Where does this support data come from?

Support levels are derived from caniemail.com, which is MIT-licensed, and are carried in the @emailens/engine package (data version 0.12.2, last synced Sep 2, 2026). Rendering behaviour described on feature pages is simulated per documented client rules, not captured from real clients.

Two dates matter here and they are not the same. The sync date, currently Sep 2, 2026, is when Emailens last copied caniemail's answers; it is anchored to a content hash of the engine's data, so it moves only when the data itself changes rather than on every release. The test dates are when someone last checked a feature in a real client, they are recorded per feature, and across this matrix they run from Feb 28, 2019 to Jul 13, 2026. 296 of 298 features carry one and each feature page shows its own.

Can I check my own HTML against this data?

Yes. Paste an email into the checker on this page and it runs every property through the same matrix, returning a per-client score with the failures listed. No account is needed.

Email CSS & HTML Support

Check CSS and HTML compatibility across 21 email clients. Support data derived from caniemail.com (MIT) - 298 features tracked.

Last synced Sep 2, 2026 - engine data v 0.12.2 - upstream test dates run Feb 28, 2019 to Jul 13, 2026, per feature

work everywhere

all 21 clients

173

need a fallback

partial or client-specific

are not safe to rely on

fail in half the field or worse

are not fully verified

no failures recorded, gaps remain

Data report

The State of Email CSS 2026

Only 6 of 298 features work in every client. See the full leaderboard, the Outlook traps, and the safe list →

Daily game

Renderle

Blink

84 supported5 partial

Features by Category

HTML Elements48

HTML Attributes22

Pseudo-Classes & Selectors34

CSS Functions8

calc clamp conic-gradient fit-content linear-gradient max min radial-gradient

CSS Properties162

!important accent-color align-items animation aspect-ratio backdrop-filter background background-blend-mode background-clip background-color background-image background-origin background-position background-repeat background-size bimi block-size border border-collapse border-image border-inline border-inline-individual border-inline-longhand border-radius border-radius-logical border-spacing bottom box-shadow box-sizing caption-side clear clip-path color color-scheme column-count columns css-comments cursor custom-properties direction display display:flex display:grid display:none empty-cells filter flex-direction flex-wrap float font font-family font-kerning font-size font-size-adjust font-stretch font-weight gap grid-template-columns height hyphenate-character hyphenate-limit-chars hyphens inert inline-size inset justify-content left letter-spacing light-dark line-height list-style list-style-image list-style-position list-style-type margin margin-block-start-end margin-inline-block margin-inline-start-end mask-image max-block-size max-height max-inline-size max-width min-block-size min-height min-inline-size min-width mix-blend-mode modern-color nesting object-fit object-position opacity orphans outline outline-offset overflow overflow-wrap padding padding-block-start-end padding-inline-block padding-inline-start-end position resize rgb rgba right scroll-snap shape-margin shape-outside system-ui tab-size table-layout text-align text-align-last text-decoration text-decoration-color text-decoration-line text-decoration-skip-ink text-decoration-style text-decoration-thickness text-emphasis text-emphasis-position text-indent text-justify text-orientation text-overflow text-shadow text-transform text-underline-offset text-underline-position text-wrap top transform transition unit-ch unit-cm unit-em unit-ex unit-in unit-initial unit-mm unit-pc unit-percent unit-pt unit-px unit-rem unit-vh unit-vmax unit-vmin unit-vw user-select vertical-align visibility white-space white-space-collapse widows width word-break word-spacing writing-mode z-index

Check your own HTML

Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.

Questions

How many CSS features work in every email client?: 6 of 298 tracked features are supported in all 21 clients we cover, as of Sep 2, 2026. 173 work somewhere but need a fallback, 91 fail in at least half the field, and 28 have no recorded failures but still carry untested clients.
Where does this support data come from?: Support levels are derived from caniemail.com, which is MIT-licensed, and are carried in the @emailens/engine package (data version 0.12.2, last synced Sep 2, 2026). Rendering behaviour described on feature pages is simulated per documented client rules, not captured from real clients.
How current is it?: Two dates matter here and they are not the same. The sync date, currently Sep 2, 2026, is when Emailens last copied caniemail's answers; it is anchored to a content hash of the engine's data, so it moves only when the data itself changes rather than on every release. The test dates are when someone last checked a feature in a real client, they are recorded per feature, and across this matrix they run from Feb 28, 2019 to Jul 13, 2026. 296 of 298 features carry one and each feature page shows its own.
Can I check my own HTML against this data?: Yes. Paste an email into the checker on this page and it runs every property through the same matrix, returning a per-client score with the failures listed. No account is needed.

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The State of Email CSS 2026

Renderle

Email Clients

Gmail

Gmail Android

Gmail iOS

Outlook 365

Outlook (New)

Outlook Classic

Outlook iOS

Outlook Android

Outlook for Mac

Apple Mail

Apple Mail iOS

Yahoo Mail

Yahoo Mail Android

Yahoo Mail iOS

Samsung Mail

Thunderbird

HEY Mail

Proton Mail

AOL Mail

Fastmail

Superhuman

Features by Category

HTML Elements48

HTML Attributes22

HTML & Email Structure8

CSS At-Rules10

Pseudo-Elements6

Pseudo-Classes & Selectors34

CSS Functions8

CSS Properties162

Check your own HTML

Check your own HTML

Questions

Test your email in Gmail, Outlook and Apple Mail