(may vary slightly by version)
You can change your default view by going to
View-> Arrange By-> Current View-> Define Views…
Here you can edit the default Messages view. Since modifying this view
doesn’t effect the folders you already have modified I recommend defining a
new view and apply that view on first use of the folder.
If you want to only disable the Preview Pane in individual folders, make sure the folder is selected. Go to ‘View’, then ‘Preview Pane’, and choose ‘off’.
source: groups.google.com
