When someone replies to a post by email, there is a small icon on the top right of his message.
When you click on it, as an admin, you have a popup with various email data.
The content is vertically scrollable, but the vertical scrollbar is hidden, which confused me at first.
I had to first scroll horizontally to make the horizontal scrollbar appear.
I think both scrollbars should be visible by default (if needed), but you shouldn’t use a scrollbar in order to make another scrollbar appear.