Microsoft has released the following patches for Exchange:
April 2004 Exchange 2000 Server post-Service Pack 3 update rollup
This patch resolves problems that were found in Exchange 2000 since SP3 was released.
Exchange 2003 Post-RTM Store Patch 6980.72
This patch resolves problems that were found in the Exchange 2003 Store since Exchange 2003 was released. [MS Exchange Blog]