Microsoft Outlook 2013 allows customizing font size used to show sender date, name and sub in message list. May be you need to just change size to make font big or small in size or change font size to one you like better.
To change font setting of Message list, Open Microsoft Outlook and Click to “View” tab
Step 1: Simply click on the “View Setting” button in Current View section of View tab.
Click on Conditional Formatting available in Advanced View Setting dialog box.