Select the message(s) you want to mark.
Open the Edit menu and choose Mark as Read.
The messages are marked as read.
Messages that have not been read are displayed in bold, but you can easily enable or disable this marking. For example, you might delete unread junk mail. So that the Deleted Items folder and the messages in it aren't displayed in bold, you can mark them as read.
Marking Messages as Unread
You can also do the reverse?mark a message as unread. You might do this if you opened a message but didn't thoroughly read the contents. To mark a message as unread, select the message, open the Edit menu, and choose Mark as Unread.