Could anybody here tell me what the default font and font sizes are for Sonoma’s Mail?
Mail > Settings > Fonts & Colors
Also, is it true that although San Francisco is the macOS’ default font, you cannot choose it as font for Mail’s message list or message contents?
This is what I have:
It is not possible to select Apple’s San Francisco font directly from application menus, though it is possible to choose it for web pages using CSS in browsers and perhaps by programmatic means or by editing settings files in certain apps. (I think “System Font Regular” is, by default, San Francisco, unless you’ve customized the default font in the Finder.)
Thank you.
That is what I have so far also gathered. But without being able to select SF, how do you go back to using it if you’ve ever selected another font? I see no obvious way to remove the selection and get back to default. I see neither SF nor System Font show up in my font list.
This is what I see when clicking Select…
Apple using Helvetica as system font used to make trouble for me as I worked with what we called “Flight Check” of customer Indesign and Quark Express documents in the 1990s at a commercial printer. Back again, I see.
You can try downloading the SF stuff separately, I think that might work
That worked. Thank you.
I’m still a bit surprised that this Mail settings GUI has neither an undo nor a return to default option. I tried finding the plist for Mail thinking I might just be able to remove my preference and have that take me back to defaults, but fat chance finding the plist with that preference. 
Quit Mail.app and type this in Terminal.app:
defaults delete -app Mail MessageListFont
It’s not elegant, but it works.
Thank you.
Interestingly enough, on my Mac although that works to restore the default, it doesn’t come back saying System Font Regular 11. No, it says Lucida Grande 13 even though it’s not showing as such (it’s actually displaying as SF). If I actually go select Lucida Grande 13, that changes the font to Lucida. Go figure. 
I can’t help Simon but in the same vein is there a way to change Mail’s heading (To: Cc: etc.) cursor color? On my Mac it’s a nearly invisible yellow. I don’t remember this being an issue before Sonoma.