CSS Properties

border-spacing

CSS property · 16 supported, 0 partial, 3 unsupported across 21 clients

16 of 21 email clients render border-spacing fully (Sep 2, 2026 data); it breaks outright in Outlook (New), Outlook Classic, Outlook for Mac.

5/7 webmail, 3/6 desktop, 8/8 mobile clients support border-spacing fully.
Unsupported in Outlook (New), Outlook Classic, Outlook for Mac.
Outlook Classic (Word engine, supported to at least 2029) does not fully support border-spacing, and its replacement changes little here; see the deprecation diff.
Documented before/after fixes on this page cover 21 clients, including Gmail and Gmail Android.
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 Dec 20, 2023, synced by Emailens Sep 2, 2026.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Supported
Gmail iOS	mobile	Gmail Mobile	Supported
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	Unsupported
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Supported
Yahoo Mail Android	mobile	Yahoo	Supported
Yahoo Mail iOS	mobile	Yahoo	Supported
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Supported
HEY Mail	webmail	WebKit	Unknown
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Supported
Fastmail	webmail	Fastmail	Unknown
Superhuman	desktop	Blink	Supported

Client-by-client behaviour for border-spacing

Fully supports border-spacing (16): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook iOS, Outlook Android, Apple Mail, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, Thunderbird, Proton Mail, AOL Mail, Superhuman.

No support (3): Outlook (New), Outlook Classic, Outlook for Mac. Plan fallbacks for these clients before relying on border-spacing in production sends.

Behaviour unverified in: HEY Mail, Fastmail.

Fixes & Workarounds

Outlook (New)

Unsupported

Use the cellspacing HTML attribute instead (e.g., <table cellspacing="8">).

Before (Broken)

before.html

3 lines

<table style="border-spacing: 8px; border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

After (Fixed)

fixed.html

3 lines

<table cellspacing="8" style="border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

Use the cellspacing HTML attribute instead of border-spacing CSS

Outlook Classic

Unsupported

Use the cellspacing HTML attribute instead (e.g., <table cellspacing="8">).

Before (Broken)

before.html

3 lines

<table style="border-spacing: 8px; border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

After (Fixed)

fixed.html

3 lines

<table cellspacing="8" style="border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

Use the cellspacing HTML attribute instead of border-spacing CSS

Outlook for Mac

Unsupported

Use the cellspacing HTML attribute instead (e.g., <table cellspacing="8">).

Before (Broken)

before.html

3 lines

<table style="border-spacing: 8px; border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

After (Fixed)

fixed.html

3 lines

<table cellspacing="8" style="border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

Use the cellspacing HTML attribute instead of border-spacing CSS

Production guidance for border-spacing

border-spacing is a CSS property. Across the email client matrix, 16 of 21 tracked clients support it fully, 0 only partially, and 3 not at all. The clients most likely to require a workaround for this feature are Outlook (New), Outlook Classic, Outlook for Mac. 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 border-spacing 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 border-spacing

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

Zero-Friction Engine Preview

Test your border-spacing layout across 21 email clients

Preview rendering, catch CSS issues, and see how border-spacing displays across Outlook, Gmail, and Apple Mail. Free, no account needed.

Instant live preview · No signup required · 21 email engines

Last tested upstream: Dec 20, 2023 · Last synced by Emailens: Sep 2, 2026

caniemail.com (MIT) records Dec 20, 2023 as the last time border-spacing was tested in a real client, 2 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.