CSS property · data last changed 10 Nov 2026
mask-image in email clients
Works in 4 of 21. Not supported in Gmail, Gmail Android, Gmail iOS and 9 more. Partial in Proton Mail. Untested in Thunderbird, HEY Mail, Fastmail and 1 more.
Your reader in Outlook Classic sees the email without mask-image, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
Pre-render any masked imagery as a PNG with the mask already baked in. Reserve mask-image for purely decorative effects layered on top of an already-complete design.
There is no drop-in fix for mask-image in Outlook Classic. Design so the email still reads without it.
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mask-image is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Gmail | Not supported |
| Gmail Android | Not supported |
| Gmail iOS | Not supported |
| Outlook 365 | Not supported |
| Outlook (New) | Not supported |
| Outlook Classic | Not supported |
| Outlook iOS | Not supported |
| Outlook Android | Not supported |
| Yahoo Mail | Not supported |
| Yahoo Mail Android | Not supported |
| Yahoo Mail iOS | Not supported |
| AOL Mail | Not supported |
| Proton Mail | Partial See caveat 1 |
| Thunderbird | Untested |
| HEY Mail | Untested |
| Fastmail | Untested |
| Superhuman | Untested |
Works in 4: Outlook for Mac, Apple Mail, Apple Mail iOS and 1 more. Show all
| Client | Support |
|---|---|
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Samsung Mail | Works |
Caveats (1)
- 1. Proton Mail: Notation using
urlis not supported.
Caveats as recorded by caniemail (MIT), one entry per wording.
How mask-image behaves
mask-image applies a mask layer to an element, hiding portions based on alpha or luminance. Email support is extremely limited, only WebKit-based Apple Mail and a few experimental clients honor it. For reliable cross-client masking effects, pre-render the masked image as a PNG.
- Outlook, Gmail, and Yahoo all ignore mask-image, design must remain visually intact without it.
- Even in Apple Mail, mask-image performance varies on older iOS versions; test before deploying.
- Combining mask-image with animation or transform produces unpredictable rendering across clients.
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