From the control pannel, open TweakUI. (it's a Microsoft "power toy")
Go down to Startup/Session oppening and devlop that item.
You'll find an "Unread message(s)" item, click it.
On the right, the first item lets you adjust if you want to show how many messages at all and for how many days unread messages are displayed.
Uncheck to disable it totaly. Adjust the number of days if you want to still have that feature but don't want older messages to be counted.
The second section lets you apply your setting to EVERY users (need administrative privilege), or only the current one.
Click OK or "Apply"
Electro, June 2011