I think I have found something in MS KB that might help you:
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SYMPTOMS
If you check your MSN, The Microsoft Network, Post Office Protocol 3 (POP3) e-mail account with Outlook or Outlook Express, you may no longer receive any new e-mail messages. You do not receive any error messages, and you can successfully send e-mail messages from your MSN POP3 account.
CAUSE
This issue can occur if you installed and ran MSN Explorer. You can download the MSN Explorer software from the following MSN Web site:
When you install the MSN Explorer software and then log on to your MSN account, your POP3 MSN e-mail messages are migrated to the new MSN Hotmail system.
MORE INFORMATION
If both of the following are true, then you are using MSN Explorer:
You start MSN and a "butterfly" icon appears by the clock on your computer (the "System Tray"

.
You right-click the butterfly icon, click System Information, and the number next to MSN Client is 6.00 or greater.
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This is an excerpt from
KB article 268732
;-)
Hope this helps,
MakeItSo
Andreas Galambos
EDP / Technical Support Specialist
Bowne Global Solutions Wuppertal, Germany
(andreas.galambos@bowneglobal.de)
HP: