font-weight

Estimated Support About

78.05% + 21.95% = 100.0%

Apple Mail

macOS

11
12
13
14
15

iOS

11
12
13
14
15

Gmail

Desktop Webmail

2021-01
2022-06

iOS

2021-01
2022-06

Android

2021-01
2022-06

Mobile Webmail

2021-01
2022-06

Outlook

Windows

2007
2
2010
2
2013
2
2016
2
2019
2

Windows Mail

2021-01
2

macOS

2021-01
16.80

Outlook.com

2021-01

iOS

2021-01

Android

4.2101.1

Yahoo! Mail

Desktop Webmail

2021-01
1

iOS

6.21.1
1

Android

6.16.2.1525679
1

AOL

Desktop Webmail

2021-01
1
2022-06
1

iOS

2021-01
1

Android

2021-01
1

Samsung Email

Android

6.1.31.2

Mozilla Thunderbird

macOS

2021-01

ProtonMail

Desktop Webmail

2021-01

iOS

2021-01

Android

2021-01

Fastmail

Desktop Webmail

2021-07

HEY

Desktop Webmail

2021-01

Orange

Desktop Webmail

2021-01
2021-03
1
2024-04
1

iOS

2021-01
2024-04

Android

2021-01
2024-04

LaPoste.net

Desktop Webmail

2021-08

SFR

Desktop Webmail

2021-01

iOS

2021-01

Android

2021-01

GMX

Desktop Webmail

2022-06

iOS

2022-06

Android

2022-06

1&1

Desktop Webmail

2022-06

Android

2022-06

Mail.ru

Desktop Webmail

2021-01
2022-06

WEB.DE

Desktop Webmail

2022-06

iOS

2022-06

Android

2022-06

WP.pl

Desktop Webmail

2025-09

Notes

  • 1

    Partial support. <number> values are not supported as per CSS Fonts Level 4 where any <number> value between 1 and 1000 (inclusive) is a valid value. Only the following numeric values are supported: 100, 200, 300, 400, 500, 600, 700, 800, and 900.

  • 2

    Partial support. <number> values between 0 and 599 are set as normal font weight. <number> values between 600 and 1000 are set as bold font weight.

Resources

Sponsor

Resend

Sponsored by Resend. Email for developers. The best way to reach humans instead of spam folders. Deliver transactional and marketing emails at scale.

Know something we don't?

Is any of the above data outdated? Or do you want to add a new email client to the list? Heads on to GitHub and edit the data file!

Edit this page on GitHub Report an issue on GitHub

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Test it yourself

This feature was last tested on June 23, 2022.

If you want to test this feature in the same conditions as we did, you can get our test code and run a test by yourself. Make sure to follow our testing recommendations first.

View the test code