Mail app font issue after macOS Tahoe 26.0 update

FIXED: Apple Mail showing wrong bold/condensed font (macOS 14)

After days of troubleshooting, I finally solved the issue — and it turned out to be a rogue installed font overriding Mail’s fallback font, not a system corruption.

If your Mail messages suddenly appear in a weird bold, condensed font, this may be your fix.

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Symptoms

• Mail ignores your chosen message font
• Plain‑text or simple emails appear in a heavy condensed sans‑serif
• Changing fonts in Mail doesn’t help
• Safe Mode doesn’t help
• Reinstalling macOS doesn’t help
• The wrong font appears even while typing

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The breakthrough

In Mail, go to:

Format → Show Fonts

This reveals the actual font Mail is using at that moment — not the one you selected in Settings.

In my case, Mail was secretly using: Helvetica Bold Condensed

This font was installed in my Font Book and was hijacking Mail’s fallback font system.

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How I fixed it

1. Open Font Book
2. Locate the rogue font (mine was Helvetica Bold Condensed)
3. Remove or disable that font
4. In Mail → Settings → Fonts & Colors, temporarily change your message font to something else (I used Arial)
5. Quit and relaunch Mail
6. Send yourself a test message
7. If everything looks normal again, you can reinstall the font you removed
8. Relaunch Mail — the issue stays fixed

Mail rebuilds its fallback font map without the rogue font, and the problem disappears.

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Why this works

Mail uses fallback fonts for plain‑text or minimally formatted messages.

If you have a condensed or bold variant installed, Mail may incorrectly choose it as the fallback.

Removing the font forces Mail to reset its fallback mapping.

Reinstalling it afterwards is safe — Mail won’t reassign it.

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If you’re seeing this issue

Open Show Fonts in Mail and check what font is actually being used.

Whatever appears there is the culprit.

Look in the folders home/library/fonts and library/fonts and remove any Helvetica copies you find there. (You can’t modify system/library/fonts)

Thanks - this was correct. Mimestream recently released an update that addressed the issue (they're great - recommend this mail app to anyone who's looking for a Gmail-based native Mac app). This was my main concern, as the Impact font bug was worst there. Outlook, no update yet, but my expectation is lower there, for obvious reasons. Maybe one day.

If I read you post correctly, it looks like you have an example of the email html font codes being treated differently in Safari and Mail, with the former being correct. I suggest you report this to Apple via

http://www.apple.com/feedback

and include a link to this discussion so they can see your images and code.

Tattoued wrote:

I just checked. There were no other copies of Helvetica there.

Do those mails display ok if you use safari webmail instead of Mail?

If you go to Mail > View > Message > Raw Source and look at the html code, can you tell what font is stipulated there but is generating the squares?

What happens if you select some squares and do Format / Show Fonts?

Yes, the fact that all is well in systems where you have not added your fonts is evidence that removing one of those will probably fix it. Anything useful in terms of font names in the incoming Raw Source?

I'm also experiencing this, also in my mail apps - Outlook and Mimestream.  Replacement of swaths of text with something that looks like Impact (horrors of horrors).   It persists in 26.2, which I just updated to.   Clearing font cache using OnyX didn't seem to help. Haven't yet reset my Font Book yet.

What about THIS problem? Only certain emails will display like this (of course it's usually the most important ones), but yet show the text correctly in the preview window. If I copy/paste the message, it reads correctly. I imagine another font issue? But which one? How do I detect that without resetting all fonts? I'm a graphic artist and have TONS of fonts active and it would be horrific to have to reactive all those fonts. Tried troubleshooting with Apple for about 2 hours with no results. Needed to try safe mode but don't have a wired keyboard so it won't work. Did try setting up an additional user with default settings and it worked, although it would be a LOT of work to migrate everything to that user profile, no? And once I activate my fonts, what if it happens again? I tried changing my mail fonts to arial and/or calibri with no luck. I didn't have this problem prior to Tahoe.

Retina 5k 27" 2020

Tahoe 26.2

whoopseez wrote:

1. After updating to macOS Tahoe 26.0 the 'default' or 'fallback' font in my Mail app does not match my system font. It appears to be Impact or some similar extra bold font. This impacts emails across the board in random spots within the message.

I already tried:

Font Utility -> Settings -> Reset Fonts -> Reboot system. The problem persists.

System info:

2024 Mac Mini M4

macOS 26.0 (25A353)

I have no idea what interface that is... maybe it is not your issue but the email received and some html you have no control(?)

From the Font Book.app>Settings>Advanced>Reset Fonts

Mail.app>Settings>Fonts

Mail.app pick fonts in mail that are part of the system fonts(?)

The current stable release of Tahoe including bug fixes, security updates is macOS 26.1

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

if this is some isolated one off issue— I think I could easily not worry about it.

Yes. Problem is that I can't identify the rogue font. It only shows boxes. I really was hoping there might be a different work around other than resetting fonts since I'm a graphic artist and REALLY need ALL my fonts open. No such luck I imagine. :(

Not sure why your other question to me isn't showing here... It SAYS it's Helvetica - the system font version that is locked. NONE of my default or viewing fonts in the mail program are set to Helvetica. I've tried Arial and Calibri and Verdana - the common default fonts - and nothing is working. It's not ALL emails. Just certain ones. I just picked out a couple of other emails from other sources that were also showing as just boxes, and they are Helvetica as well! All the others that are showing correctly are other fonts - Segoe, Arial, Calibri, etc. So... Can I delete Helvetica from the system font folder and somehow reinstall it or is this a Mail issue?

The emails display fine on my iPad and on my iPhone. It’s only on my iMac that I have this problem. I’m not in front of my computer at the moment but I’ll check that raw source first thing in the a.m.!

No. I’m sure it’s a font issue, but not sure how to track it down without resetting fonts and adding back in one at a time, which will be VERY time consuming. I appreciate your help. I didn’t get many results from my 2 hour consultation with Apple.

Not that I could tell. There were several fonts named, but none were that in my font book. I’m going to look again, though, since there was a lot of code in that raw source. Fonts will always be in parentheses, right?