You can mark messages that you receive as important, to visually mark the message in your message list. When you mark a message as important, the message header information changes color, and an exclamation-point icon is displayed in the Important column.
To mark a message as important, select the message in the message list. Choose Edit -> Mark as Important.
To mark a message as normal, select the message in the message list. Choose Edit -> Mark as Unimportant.