а почему бы вам не установить fix?http://support.microsoft.com/kb/183481
Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0.
A supported fix is now available, but has not been fully regression- tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.
This fix has been posted to the following Internet location:
ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixe.../ (ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixe.../)
Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.5. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.5. For information about obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):
S E R V P A C K