To turn off the preview pane in Windows Mail/Outlook Express proceed as follows:
Click View Menu
Select Layout
When the window opens uncheck the box marked 'Show preview pane'
Click 'Apply' then 'OK'
How do I disable the Message pane in Thunderbird?
To turn off the preview pane in Thunderbird proceed as follows:
Click View Menu
Select Layout
Make sure that 'Message pane' does not have a marker against it - if it has click 'Message pane' to remove it.
In Outlook proceed as follows.
On the View menu, point to Reading Pane, and then click off.