How do I keep Inbox line highlighted if I click mouse in the email

I have Outlook 2003. When I click on an email in the inbox that I want to
read, that line in the inbox turns blue and I can read the contents of the
email in the area below the inbox messages. When I move my mouse/cursor down
into the actual body of the email message I am reading and I click the mouse
(for example if I click to open and attachment) the blue that was
highlighting the email line above is no longer blue and it's hard to tell
exactly which email I have open. How do I set outlook to leave that message
line blue if I click in the actual body of the message itself.