CSS property · data last changed 10 Nov 2026
font-size in email clients
Works in 13 of 21. Partial in Outlook Classic, Yahoo Mail, Yahoo Mail Android and 3 more. Untested in HEY Mail and Fastmail.
Your reader in Outlook Classic may not see font-size the way you wrote it, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
Use absolute units (px) over em or rem in email for predictable rendering. Set font-size on every text-bearing element rather than relying on inheritance, since some clients reset font-size at table boundaries.
- Partial support.
remvalues are not supported. - Partial support.
relativeandpercentagesize values not supported.
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font-size is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Outlook Classic | Partial See caveat 1 |
| Yahoo Mail | Partial See caveat 2 |
| Yahoo Mail Android | Partial See caveat 2 |
| Yahoo Mail iOS | Partial See caveat 2 |
| Samsung Mail | Partial See caveat 3 |
| AOL Mail | Partial See caveat 2 |
| HEY Mail | Untested |
| Fastmail | Untested |
Works in 13: Gmail, Gmail Android, Gmail iOS and 10 more. Show all
| Client | Support |
|---|---|
| Gmail | Works |
| Gmail Android | Works |
| Gmail iOS | Works |
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Thunderbird | Works |
| Proton Mail | Works |
| Superhuman | Works |
Caveats (3)
- 1. Outlook Classic: Partial support.
remvalues are not supported. Partial support.relativeandpercentagesize values not supported. - 2. Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: Partial support.
remvalues are not supported. - 3. Samsung Mail: Partial support.
relativeandpercentagesize values not supported.
Caveats as recorded by caniemail (MIT), one entry per wording.
How font-size behaves
font-size sets the rendered size of text in email and is supported universally, but client-specific minimum-font-size settings can override your declaration. Apple Mail iOS, for example, may upscale anything below 13-14px to improve legibility, breaking carefully tuned typographic hierarchies.
- Apple Mail iOS auto-enlarges text below ~13px for accessibility, regardless of your declared size.
- Gmail Android sometimes scales text proportionally when the user has accessibility text-size settings enabled.
- Older Outlook builds inherit Word's font-size logic, which can compound nested em-based sizes unexpectedly.
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