This article is about the steps required for changing the font size of folder name in Outlook 2016, 2013 and 2010. If you think the font size of folders in Outlook is small to read then you can use the below mentioned steps to increase the font size.
Click the File menu then Options link. In the Option Windows, click the Advanced tab and navigate to Outlook Panes section.
Then launch the Navigation Pane Options by clicking Navigation Pane button.
In the Navigation Pane Options, click the Font button and select your desired font size. Click Ok button to confirm and save the changes.
Now all your Folders name in Outlook 2010 navigation pane will be reflected in the changed font size. Please note that this would affect all the items in the navigation pane and not just the folder name.