Font settings for reading messages

I have trouble understanding the settings under Menu > Settings > Mail > Read > Preferred Style. My settings look like this:

2021-01-31_162142

The effect seems to be that

  • My selected font and size “Calibri; 11 pt” is used for HTML messages where no font is defined in the HTML code,

  • As I have unchecked the option “Use preferred font for fixed-width plain text messages”, a fixed width font rather than the selected “Calibri; 11 pt” is used to display plain text messages.

So far, so good. My question is, how does eM Client select the fixed width font to display plain text messages? Is it possible to change it somewhere, or is it a Windows 10 setting that applies to all applications? If so, where would I find that setting in Windows?