CSS property · 10 real installs 14 Oct 2026 · data last changed 10 Nov 2026
border-collapse in email clients
Works in 19 of 21. Untested in HEY Mail and Fastmail.
caniemail (MIT) via @emailens/engine 0.18.22
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border-collapse on 10 real installs
One Emailens probe, screenshotted on each install on 14 October 2026, next to our live preview of the same client. Where border-collapse is supported you should see: single lines between cells.
caniemail: border-collapse works in Outlook Classic.
caniemail: border-collapse works in Outlook 365.
This Outlook.com install drops the <style> in the head, so only inline styles apply.
caniemail: border-collapse works in Apple Mail.
caniemail: border-collapse works in Apple Mail iOS.
caniemail: border-collapse works in Yahoo Mail.
Also captured, not counted as evidence (3)
- Outlook for Microsoft 365 · not mapped to an engine client yet Real screenshot
- Outlook 2019 for Mac (legacy app) · not counted as Outlook for Mac Real screenshot
This is the legacy Outlook for Mac app. The new Outlook for Mac, which the table describes, drops gradients, grid sizing functions, var() and more.
- Gmail (web) · not counted as Gmail Real screenshot
This Gmail install does not apply Gmail's sanitiser, so it shows more than real Gmail does.
Every account includes one free real-device check in classic Outlook, Outlook for Mac and Apple Mail, after you verify your email and run one preview, while this month's free capacity lasts. How real-device checks work →
All 21 clients, problems first
| Client | Support |
|---|---|
| HEY Mail | Untested |
| Fastmail | Untested |
Works in 19: Gmail, Gmail Android, Gmail iOS and 16 more. Show all
| Client | Support |
|---|---|
| Gmail | Works |
| Gmail Android | Works |
| Gmail iOS | Works |
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook Classic | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Yahoo Mail | Works |
| Yahoo Mail Android | Works |
| Yahoo Mail iOS | Works |
| Samsung Mail | Works |
| Thunderbird | Works |
| Proton Mail | Works |
| AOL Mail | Works |
| Superhuman | Works |
How border-collapse behaves
border-collapse controls whether adjacent table-cell borders share a single line or render as separate boxes. In email, it is essential to set border-collapse: collapse on every layout table to prevent unwanted gaps between cells in Outlook and Yahoo.
- Without border-collapse: collapse, Outlook Classic can render visible gaps between cells even when cellspacing="0" is set.
- Outlook 2007-2019 sometimes ignores border-collapse on nested tables, apply it explicitly to every <table>.
- border-collapse: separate enables border-spacing, but border-spacing itself is poorly supported in Outlook.
Always set border-collapse: collapse via inline style on every layout <table>. Combine with cellspacing="0" cellpadding="0" border="0" attributes for full Outlook coverage.
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