On the Read tab, select the following check box: Message is read after being previewed 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.
Tips
To mark an individual message as read or unread, click the Edit menu, and then click Mark as Read or Mark as Unread.
To mark all the messages in a newsgroup thread as read, click any message in the thread, click the Edit menu, and then click Mark Thread as Read. A thread is an original message and any posted replies. Threads are sorted and grouped according to the title. For example, a thread that starts with a message titled "Tips for Labrador owners" includes all of the replies titled "RE: Tips for Labrador owners."