There are two ways to temporarily increase or decrease the zoom level in the Microsoft Outlook Reading Pane.
Do one of the following:
Use the Zoom control at the bottom of the Outlook window.
If you are using a mouse with a wheel control, click in the Reading Pane, press CTRL, and roll the scroll wheel. Rolling the wheel away from you makes the contents larger, rolling the wheel toward you makes the contents smaller.
Note: The zoom affects only the current item that is previewed. When you select another item or folder, the Reading Pane returns to the default 100% size.