Using classic Outlook for Windows in business environments
I don't know if this has been fixed yet, but...
If you're using Outlook (classic), go to View -> Layout - > Reading Pane -> Right
This brought back the reading Pane in one window, as opposed to it opening in a new window.
I figured since this had 1201 people who had the same question, I thought I should put this question to rest, once and for all.