Accidentally changed the default font of macOS Mail.app, and was super surprised to see there’s no option to “reset to defaults”. Plus, there’s no other ways to select a “system font”.
Found the following post StackExchange - How do I choose “System Font” in the font picker? to work around. Also improvised a little bit to reset both fixed-width and message fonts. (You need to view the binary file at
~/Library/Containers/com.apple.mail/Data/Library/Preferences/com.apple.mail.plist to identify the attribute names but I’ve done the heavy lifting for you.)
defaults delete -app Mail NSFont defaults delete -app Mail NSFixedPitchFont defaults delete -app Mail MessageListFont defaults delete -app Mail NSFixedPitchFontSize defaults delete -app Mail NSFontSize