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Does CSS box-sizing Work in HTML Email?
Controls whether padding and border are included in an element's total width and height calculation.
Quick Answer
Does box-sizing work in HTML email?
The CSS box-sizing property is supported in Gmail, Outlook (Mac / Web), Apple Mail, Samsung Email, and others. It is NOT supported in Outlook (Windows), Yahoo! Mail. Always include a safe fallback for unsupported clients.
Which Email Clients Support CSS box-sizing?
CSS support for box-sizing 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 | ✗ No | ✗ No | — |
| Samsung Email | ? | ✓ Yes | — |
| Thunderbird | ✓ Yes | ? | — |
| ProtonMail | ✓ Yes | ✓ Yes | — |
| Fastmail | ✓ Yes | ? | — |
Frequently Asked Questions
Test Your Email Now
Paste your HTML and see how it renders in clients that don't support box-sizing.
Building a new email instead of checking an existing one? MailViewr's Email Builder only lets you use CSS that's known to render across clients, so box-sizing can't sneak into your markup by accident. Open the Email Builder →