Unified Folders

Unified Folders combines folders from more than one account. By clicking View > Folders you can use the radio buttons to select the view that you want:

Unified - combines all of your mailboxes from several accounts into one view. 

All - provides separate folders for each mail account:

Unread - shows all folders with unread messages:

Favorite - shows your favorite folders:

Recent - shows the most recently used folders

Another option for changing the folders view is to use the arrows located just above the folders area.  

This allows you to cycle through the different view options.