In your message list, Outlook will now use a larger font to display the sender’s name and a smaller font to display the subject of the message. To change this font size, you can create an additional Conditional Formatting rule without any conditions but with its font settings to smaller.
- tab View-> button View Settings-> button Conditional Formatting…
- Click Add.
- Name the rule. For instance: Standard font size
- Click the Font… button.
- Set the desired size
- OK yourself out of the open dialogs and confirm that you indeed want to create this rule without any conditions.