CSS property · data last changed 10 Nov 2026
!important in email clients
Works in 11 of 21. Partial in Gmail, Gmail Android, Gmail iOS and 6 more. Untested in Superhuman.
Your reader in Outlook Classic may not see !important the way you wrote it, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
- Partial. Only supported with a space before.
- Partial. Not supported inline. (See email-bugs#31)
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 →
!important is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Gmail | Partial See caveat 1 |
| Gmail Android | Partial See caveat 2 |
| Gmail iOS | Partial See caveat 2 |
| Outlook Classic | Partial See caveat 3 |
| Yahoo Mail | Partial See caveat 4 |
| Yahoo Mail Android | Partial See caveat 4 |
| Yahoo Mail iOS | Partial See caveat 4 |
| Proton Mail | Partial See caveat 5 |
| AOL Mail | Partial See caveat 4 |
| Superhuman | Untested |
Works in 11: Outlook 365, Outlook (New), Outlook iOS and 8 more. Show all
| Client | Support |
|---|---|
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Samsung Mail | Works |
| Thunderbird | Works |
| HEY Mail | Works |
| Fastmail | Works |
Caveats (5)
- 1. Gmail: Partial. Only supported in lowercase. (See email-bugs#13)
- 2. Gmail Android, Gmail iOS: Partial. Only supported in lowercase. (See email-bugs#13) Partial. Only supported inline when using a Non Gmail Account due to the lack of
<style>support. - 3. Outlook Classic: Partial. Only supported with a space before. Partial. Not supported inline. (See email-bugs#31)
- 4. Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: Partial. Removed if there is no space before when used with a
background-imageproperty. (See email-bugs#16) - 5. Proton Mail: Partial. Only supported in lowercase. Partial. Only supported if not written in lowercase. Partial. Only supported inline due to the lack of
<style>support.
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.