First demark under Tools - Options... - General settings - Basic settings: 'Save the Pegasus Mail desktop state between sessions'.
Close Pegasus Mail, start it and take care the Three-pane window is not maximised.
Make your settings, close Pegasus Mail, start it again maximise the Three-pane window and mark Save the Pegasus Mail desktop state between sessions.

Succes.

In all but the new mail folder, column widths always return to the narrowest possible on the left, cutting off much of the text in each column including even the first digit of the message date.  I have tried all the choices I can find in folder options with no success.

 How do I save my preferred widths once I have set them?

 Thanks.