I agree with this but also that it is too many steps to turn preview mode off/on. It is currently six steps for each:
- Click grid
- Click settings
- Click preview pane
- Click None
- Click Save
- Click mail
This should be an option right on the toolbar to turn on/off. This would go from 6 steps to 1 (2 if you decide to make it in a sub menu -- not recommended).