The reading pane, sometimes called the preview pane, lets you read items without opening them. You can customize the reading pane according to your preferences. The reading pane can be positioned on the right of the Outlook window, below the item list, or hidden.
On the Organize tab, click Reading Pane, and then click an option.
Note: To change the size of the reading pane, rest the pointer on the border between the reading pane and the item list, and then drag the border.