CSS Properties

display:flex

CSS property · 17 supported, 2 partial, 2 unsupported across 21 clients

17 of 21 email clients render display:flex fully (Sep 2, 2026 data); it breaks outright in Outlook (New), Outlook Classic.

7/7 webmail, 4/6 desktop, 6/8 mobile clients support display:flex fully.
Unsupported in Outlook (New), Outlook Classic.
Partial in Gmail Android, Gmail iOS, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support display:flex, and its replacement changes little here; see the deprecation diff.
Documented before/after fixes on this page cover 1 client, including Outlook Classic.
Across all clients, only 6 of 298 tracked HTML/CSS features render identically everywhere.

Source: caniemail.com (MIT), via the Emailens engine. Last tested upstream Nov 2, 2021, synced by Emailens Sep 2, 2026.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Partial^{See caveat 1}
Gmail iOS	mobile	Gmail Mobile	Partial^{See caveat 1}
Outlook 365	webmail	Outlook Web	Supported
Outlook (New)	desktop	Outlook Web	Unsupported
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Supported
Outlook Android	mobile	Outlook Mobile	Supported
Outlook for Mac	desktop	WebKit	Supported
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Supported^{See caveat 2}
Yahoo Mail Android	mobile	Yahoo	Supported^{See caveat 2}
Yahoo Mail iOS	mobile	Yahoo	Supported^{See caveat 2}
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Supported
HEY Mail	webmail	WebKit	Supported
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Supported^{See caveat 2}
Fastmail	webmail	Fastmail	Supported
Superhuman	desktop	Blink	Supported

Documented caveats (2)

1.Gmail Android, Gmail iOS: Not supported with non Google accounts.
2.Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: display:inline-flex is not supported.

Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.

Client-by-client behaviour for display:flex

Fully supports display:flex (17): Gmail, Outlook 365, 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.

Partial support (2): Gmail Android, Gmail iOS. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (2): Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on display:flex in production sends.

Fixes & Workarounds

Outlook (New)

Unsupported

Use <table> layouts for email client compatibility.

Outlook Classic

Unsupported

Use <table> layouts with <!--[if mso]> conditional comments for Outlook's Word engine.

Before (Broken)

before.html

4 lines

<div style="display: flex; gap: 16px;">
  <div style="flex: 1;">Column 1</div>
  <div style="flex: 1;">Column 2</div>
</div>

After (Fixed)

fixed.html

13 lines

<!--[if mso]>
<table role="presentation" width="100%" cellpadding="0"
  cellspacing="0" border="0"><tr>
  <td width="50%" valign="top">Column 1</td>
  <td width="50%" valign="top">Column 2</td>
</tr></table>
<![endif]-->
<!--[if !mso]><! -->
<div style="display: flex; gap: 16px;">
  <div style="flex: 1;">Column 1</div>
  <div style="flex: 1;">Column 2</div>
</div>
<!-- <![endif]-->

Use table layout as fallback for flexbox in Outlook

Gmail Android

Partial

Use <table> layouts for email client compatibility.

Gmail iOS

Partial

Use <table> layouts for email client compatibility.

Production guidance for display:flex

display:flex is a CSS property. Across the email client matrix, 17 of 21 tracked clients support it fully, 2 only partially, and 2 not at all. The clients most likely to require a workaround for this feature are Outlook Classic. Each of them needs a tailored fallback. See the per-client examples above for the specific code fix Emailens recommends.

When in doubt, ship a baseline that renders without display:flex and treat it as progressive enhancement on clients where support is verified. Emailens automatically detects cross-client divergence on this feature when you preview an email, so you can see exactly which template paths break before a campaign goes out.

Related Features

!important accent-color align-items animation aspect-ratio backdrop-filter background background-blend-mode

Check your own HTML for display:flex

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

Zero-Friction Engine Preview

Test your display:flex layout across 21 email clients

Preview rendering, catch CSS issues, and see how display:flex displays across Outlook, Gmail, and Apple Mail. Free, no account needed.

Instant live preview · No signup required · 21 email engines

Last tested upstream: Nov 2, 2021 · Last synced by Emailens: Sep 2, 2026

caniemail.com (MIT) records Nov 2, 2021 as the last time display:flex was tested in a real client, 4 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.