CSS property · data last changed 10 Nov 2026
system-ui in email clients
Works in 12 of 21. Not supported in Outlook Classic. Partial in Gmail Android, Outlook Android, Yahoo Mail Android and 4 more. Untested in Superhuman.
Your reader in Outlook Classic sees the email without system-ui, 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 system-ui in Outlook Classic. Design so the email still reads without it.
No signup · Five clients free, Outlook Classic included · All 21 with an account
The checker needs a computer screen.
A free account opens all 21 clients and keeps your checks for 7 days. Create a free account →
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 →
system-ui is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Outlook Classic | Not supported |
| Gmail Android | Partial See caveat 2 |
| Outlook Android | Partial See caveat 2 |
| Yahoo Mail Android | Partial See caveat 2 |
| Samsung Mail | Partial See caveat 2 |
| Thunderbird | Partial See caveat 2 |
| Proton Mail | Partial See caveat 2 |
| AOL Mail | Partial See caveat 2 |
| Superhuman | Untested |
Works in 12: Gmail, Gmail iOS, Outlook 365 and 9 more. Show all
| Client | Support |
|---|---|
| Gmail | Works See caveat 1 |
| Gmail iOS | Works |
| Outlook 365 | Works See caveat 1 |
| Outlook (New) | Works See caveat 1 |
| Outlook iOS | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Yahoo Mail | Works See caveat 1 |
| Yahoo Mail iOS | Works |
| HEY Mail | Works See caveat 1 |
| Fastmail | Works See caveat 1 |
Caveats (2)
- 1. Gmail, Outlook 365, Outlook (New), Yahoo Mail, HEY Mail, Fastmail: Partial. Depends on browser support.
system-uiworks in all browsers.ui-serif,ui-sans-serif,ui-roundedandui-monospaceare supported on all browsers on iOS and Safari on MacOS. - 2. Gmail Android, Outlook Android, Yahoo Mail Android, Samsung Mail, Thunderbird, Proton Mail, AOL Mail: Partial. Supports
system-uionly.
Caveats as recorded by caniemail (MIT), one entry per wording.
Your next question
- Does word-break work in Outlook Classic?
Works in 4 of 21 · partial in 12 · not supported in 5
fix - Does display:flex work in Outlook Classic?
Works in 18 of 21 · partial in 2 · not supported in 1
fix - Does display:grid work in Outlook Classic?
Works in 18 of 21 · partial in 2 · not supported in 1
fix - Does border-spacing work in Outlook Classic?
Works in 17 of 21 · not supported in 2 · 2 untested
fix - Does border-radius work in Outlook Classic?
Works in 16 of 21 · partial in 4 · not supported in 1
fix - Does visibility work in Outlook Classic?
Works in 13 of 21 · not supported in 8
fix
Every feature in Outlook Classic · All email CSS features · What real installs show
Paste your email
Get new email CSS fixes by email.