Font size for email

I know we can use control -/+ to enlarge the font of an email once the email is opened and expanded. However is there a way to expand the font globally on the display of emails from the main email screen, without having to actually double click on a single email to view it?

You can do it the same way. Right-click in the message preview and choose Zoom > Increase, or click in the message preview and use Ctrl + +.