Navigation Pane Missing

I apologise in advance if this is an easy one, but I’ve had a look and can’t find an answer:

I have a user who cannot see the navigation pane when they open their inbox. When I open their mail file from my machine I can see this pane.

I know you can resize the pane by dragging it, but that is not what is wrong in this case. Is there a setting somewhere that I am missing?

Many thanks.

Subject: Navigation Pane Missing

I found the answer. I needed to replace the Bookmark.