How do I get the new mail icon to show when new mail arrives?

[quiznos]

In Windows XP (and others) normally when a new mail message arrives in my
outlook folder, I get a new envelope-looking icon on the right-hand side of
the taskbar that show there is new mail. I accidentally clicked on it and
closed it and now I can't get it to come back, when new mail arrives. How do
I bring it back?

Thanks.