Automatically marking messages as read

On the Tools menu, click Options.
On the Read tab, select the following check box: Mark message read after displaying for x second(s).
To mark all newsgroup messages as read when you quit Outlook Express or go to another newsgroup, select the following check box: Mark all messages as read when exiting a newsgroup.

To mark an individual message as read or unread, select the message, click the Edit menu, and then click Mark as Read or Mark as Unread.
To mark all the messages in a given newsgroup conversation* as read, select either the original message or any of its replies, click the Edit menu, and then click Mark Conversation as Read.
*A conversation is an original message and all its posted replies. Conversations are sorted and grouped according to the title of the original message. For example, a conversation that starts with a message titled "Tips for Labrador owners" includes all of the replies titled "RE: Tips for Labrador owners."