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Does CSS outline Work in HTML Email?
Sets a line outside of the element's border.
Quick Answer
Does outline work in HTML email?
The CSS outline property is supported in Gmail, Outlook (Mac / Web), Apple Mail, Yahoo! Mail, and others. It is NOT supported in Outlook (Windows). Always include a safe fallback for unsupported clients.
Which Email Clients Support CSS outline?
CSS support for outline across email clients
| Email Client | Desktop | Mobile / Web | Notes |
|---|---|---|---|
| Gmail | ✓ Yes | ✓ Yes | — |
| Outlook (Windows) | ✗ No | ? | — |
| Outlook (Mac / Web) | ✓ Yes | ✓ Yes | — |
| Apple Mail | ✓ Yes | ✓ Yes | — |
| Yahoo! Mail | ✓ Yes | ✓ Yes | — |
| Samsung Email | ? | ✓ Yes | — |
| Thunderbird | ✓ Yes | ? | — |
| ProtonMail | ✓ Yes | ✓ Yes | — |
| Fastmail | ✓ Yes | ? | — |
WebKit renders square outline even when using `border-radius`.
Frequently Asked Questions
Test Your Email Now
Paste your HTML and see how it renders in clients that don't support outline.