This situation has been asked for me before, I can't find this post, and the description of the problem is like this:
When some users have access to their Microsoft Exchange 2000 Server or Microsoft Exchange Server 5.5 mailbox, the following symptoms are encountered:
The email still retains in the Microsoft Outlook "Outbox" folder of the user. The Store.exe process on the Exchange computer takes up a lot of CPU time. If you terminate the MapISP32.exe process on the user's computer, the CPU usage on the Exchange computer will return to the expected level.
Solve, you can see this KB of MS:
Http://support.microsoft.com/default.aspx?scid=kb;zh-cn;822044
