Messages that you opened are marked as read and are changed from bold to regular text. .
Click the check box to select the messages) to be marked as unread.
In the More Actions pull-down menu, select Mark as unread.
Click Go. The selected messages) are made bold and the checkmark is removed.
To mark all messages in a conversation as unread, select the conversation. To mark an individual message in a conversation as unread, open the conversation and select the message.
You can use the same method to mark unread mail as read.