In addition to the blue dot, you can have Postbox render unread emails fully bold in the message list — even in vertical view.
Have Unread Messages Highlighted in Bold in the Postbox Vertical View
To see unread email's subjects highlighted with bold face in the vertical (as they are in the traditional) view in Postbox:
- Select Tools | Options… or Postbox | Preferences… (Mac) from the menu in Postbox.
- Open the Advanced category.
- Make sure you are on the General tab.
- Click Config Editor… under Advanced Configuration.
- Now click I'll be careful, I promise! if you are prompted.
- Type "vertical.bold_unread" (not including the quotation marks) under Filter:.
- Double-click pb.thread_pane.vertical.bold_unread so that true appears under Value.
- Double-click (again) so that false appears under Value to disable unread message bolding in vertical view.
- Close the about:config and Advanced preferences windows.
(Updated July 2011)