CSS property · data last changed 10 Nov 2026
tab-size in email clients
Works in 8 of 21. Not supported in Gmail, Gmail Android, Gmail iOS and 6 more. Untested in Thunderbird, HEY Mail, Fastmail and 1 more.
Your reader in Outlook Classic sees the email without tab-size, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
There is no drop-in fix for tab-size in Outlook Classic. Design so the email still reads without it.
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tab-size is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Gmail | Not supported |
| Gmail Android | Not supported |
| Gmail iOS | Not supported |
| Outlook Classic | Not supported |
| Outlook Android | Not supported |
| Yahoo Mail | Not supported |
| Yahoo Mail Android | Not supported |
| Yahoo Mail iOS | Not supported |
| AOL Mail | Not supported |
| Thunderbird | Untested |
| HEY Mail | Untested |
| Fastmail | Untested |
| Superhuman | Untested |
Works in 8: Outlook 365, Outlook (New), Outlook iOS and 5 more. Show all
| Client | Support |
|---|---|
| Outlook 365 | Works See caveat 1 |
| Outlook (New) | Works See caveat 1 |
| Outlook iOS | Works |
| Outlook for Mac | Works See caveat 1 |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Samsung Mail | Works |
| Proton Mail | Works |
Caveats (1)
- 1. Outlook 365, Outlook (New), Outlook for Mac: Supports
tab-sizebut strips the tab character	
Caveats as recorded by caniemail (MIT), one entry per wording.
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