How to Have Unread Messages Highlighted in Bold in the Postbox Vertical View

Men pace through the night in their pounded silk kimonos when they come to visit a lady.
The regular and formal dresses' silk would swish and rustle too much, alerting everybody around in 11th-century Japan.
In 21st-century Postbox, do you want new emails to race in wearing their pounded silk — or do you prefer them to dress more boldly?
›› Like your unread messages bold in the message list? Here's how to set up Postbox so that new mail is shown with a bold face and font — including the subject line and including vertical view.