Usually..., you will just "select the mail you want to read" from the Sender, Subject, Date Pane.

But Netscape has some "fancy features" that might be of some value.
From the Netscape Mail Window Toolbar..., you can "jump to" the Next Message (or Previous Message) by:

Choosing Go, then Next Message (or Previous Message)

Notice that you can (also) "jump to"

• The Next Unread or the Previous Unread and...,
• The First Flagged, Next Flagged, or Previous Flagged Messages.

These features are "of value" to the user with "over 20" e-mail messages a day!