Partially solved my own problem....found that if I widened the folders pane, I could see an icon that switches from the list mode to preview mode.  The icon may be new?  In any case, it was hidden due to the narrow pane.  I still find no menu item to do the same thing.  Maybe it has been replaced by the icon?

 I cannot figure why anyone would want to permanently choose (or disable) either the list or the preview, given that preview is automatically turned off if certain errors occur.
 

Recently had to reinstall Pegasus Email.  Since then I cannot find the old menu item that enabled me to click on Preview to select it as message mode or de-select it as the case may be.

 Unable to find the explanation of the parameter in help nor anything in FAQ that gives me a clue on how to switch the new mail folder from what is apparently "list" to "preview".   What happened to this feature and how do I turn it on, if it still exists?

Thanks!