You can use the Reading Pane to preview messages in your Inbox and other folders.
By default, viewing messages in the Reading Pane is on. You can turn it off on toolbar View. You can customize the location of the Reading Pane.
The Reading Pane can display either at the bottom of the Content pane or on the right of the Content pane.
Click View on the Mail toolbar.
Select to display the Reading Pane either on the bottom or on the right of the Content pane. You can also turn the Reading Pane off.
The Reading Pane is empty until you click on a message.
Adjust the size of the Reading Pane by placing your pointer on top of the line between the Content pane and the Reading Pane. The pointer turns into an two-way arrow. Click on the pointer and drag to change the size of the Reading Pane area.
When you click a message in the list, the message text displays in the Reading Pane.
In Preferences>Mail, you can configure whether you want messages you view in the Reading Pane to be marked as read or not marked as read.
Mark it read immediately. As soon as you click a message in the Reading Pane it is marked as read.
Mark it read after "x" seconds. The default is 5 seconds. If you click on a message and view it for 5 seconds, the message is marked as read.
Do not mark it read. Messages you read in the Reading Pane are never marked as read.