Display Unread Messages in Bold when in Vertical View
By default, unread messages in vertical view show a blue dot to the left of the message, but do not appear in a bold typeface. If you'd like messages to display in bold when using Vertical View, you can do so by changing a hidden preference in the Config Editor.
To do this, launch the Config Editor, and search for:
and change the value to true. To revert to the default setting, change the value back to false.