In Mac OS X 10.7 Lion, Apple introduced a new interface for the Mail application. It mimics the Mail application on the iPhone and iPad. If you want to revert back to the Classic Mail interface, you have the option to. This is how:
- Open Apple Mail.
- Click Mail at the upper-left corner of your menu bar on the Mac.
- Choose Preferences.
- Select the Viewing tab.
- Check the first box at the top of the list called Use classic layout (screenshot below).