You mean "Corporate/Workgroup" mode? It's one of two mail configuration modes for OUtlook 2000, the other being Internet Only. For more information, see http://www.slipstick.com/outlook/choosingmode.htm
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Sue Mosher, Outlook MVP
Outlook and Exchange solutions at http://www.slipstick.com
Author of
Microsoft Outlook Programming: Jumpstart
for Administrators, Power Users, and Developers