Does CSS block-size & inline-size Work in HTML Email?
Defines the horizontal or vertical size of an element's block, depending on its writing mode.
Does block-size & inline-size work in HTML email?
The CSS block-size & inline-size property is supported in Apple Mail, Samsung Email, Thunderbird, ProtonMail, and others. It is NOT supported in Gmail, Outlook (Windows), Outlook (Mac / Web), and others. Always include a safe fallback for unsupported clients.
Which Email Clients Support CSS block-size & inline-size?
CSS support for block-size & inline-size across email clients
| Email Client | Desktop | Mobile / Web | Notes |
|---|---|---|---|
| Gmail | ✗ No | ✗ No | — |
| Outlook (Windows) | ✗ No | ? | — |
| Outlook (Mac / Web) | ✗ No | ✗ No | — |
| Apple Mail | ✓ Yes | ✓ Yes | — |
| Yahoo! Mail | ✗ No | ✗ No | — |
| Samsung Email | ? | ✓ Yes | — |
| Thunderbird | ✓ Yes | ? | — |
| ProtonMail | ✓ Yes | ✓ Yes | — |
| Fastmail | ✓ Yes | ? | — |
Frequently Asked Questions
Related CSS Properties
Test Your Email Now
Paste your HTML and see how it renders in clients that don't support block-size & inline-size.
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 block-size & inline-size can't sneak into your markup by accident. Open the Email Builder →