You can use the Reading Pane to preview messages in your Inbox and other folders. If you have the Reading Pane on, when you click on an email message, the message displays in the Reading Pane and the message is marked as read. To adjust the size of the Reading Pane, place your pointer on the divider bar and drag the bar.
The Reading Pane lets you read email messages from your Inbox without opening the email. Depending on your view, the Reading Pane can be at the bottom or on the right, or turned off.
You can also select whether messages you view in the Reading Pane are marked as read or not marked as read.