CSS property · data last changed 10 Nov 2026
max-block-size in email clients
Works in 5 of 21. Not supported in Gmail, Gmail Android, Gmail iOS and 9 more. Untested in Thunderbird, HEY Mail, Fastmail and 1 more.
Your reader in Outlook Classic sees the email without max-block-size, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
There is no drop-in fix for max-block-size in Outlook Classic. Design so the email still reads without it.
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max-block-size 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 Android | Not supported |
| Outlook for Mac | Not supported |
| Yahoo Mail | Not supported |
| Yahoo Mail Android | Not supported |
| Yahoo Mail iOS | Not supported |
| AOL Mail | Not supported |
| Thunderbird | Untested |
| HEY Mail | Untested |
| Fastmail | Untested |
| Superhuman | Untested |
Works in 5: Outlook iOS, Apple Mail, Apple Mail iOS and 2 more. Show all
| Client | Support |
|---|---|
| Outlook iOS | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Samsung Mail | Works |
| Proton Mail | Works |
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fix
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