How many email clients support @font-face?

It works in 6 of 21, not supported in 15.

Does @font-face work in Apple Mail?

@font-face works in Apple Mail. Closest to Proton Mail: Apple Mail, which agrees on 203 of the 300 features both are tested on.

@font-face in Proton Mail

Not supported @font-face is not supported in Proton Mail.

Works in 6 of 21 · not supported in 15

Which clients

Works: Apple Mail, Apple Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Superhuman
Not supported: Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Proton Mail, AOL Mail, Fastmail

Your reader in Proton Mail sees the email without @font-face, even if it looks right where you tested it.

What to do instead in Proton Mail

Add web-safe font fallback stack

instead

8 lines

/* Keep @font-face for clients that support it */
@font-face {
  font-family: 'CustomFont';
  src: url('custom.woff2') format('woff2');
}
h1 {
  font-family: 'CustomFont', Arial, Helvetica, sans-serif;
}

Show the original

before

5 lines

@font-face {
  font-family: 'CustomFont';
  src: url('custom.woff2') format('woff2');
}
h1 { font-family: 'CustomFont'; }

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What Proton Mail does with @font-face

@emailens/engine 0.18.22 on the original code

Proton Mail does not support "@font-face".

Your next question

Every feature in Proton Mail · @font-face in every client

Questions

How many email clients support @font-face?: It works in 6 of 21, not supported in 15.
What do I use instead of @font-face in Proton Mail?: Add web-safe font fallback stack.
Does @font-face work in Apple Mail?: @font-face works in Apple Mail. Closest to Proton Mail: Apple Mail, which agrees on 203 of the 300 features both are tested on.

To see what else in your email Proton Mail does not support, paste the whole email.

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caniemail (MIT) via @emailens/engine 0.18.22 · tested upstream 19 Dec 2023 · data last changed 10 Nov 2026 · Outlook (New) cells are the engine's mapping