Outlook 2003 (connected to Exchange 2010) gives unknown error when deleting some messages

When users delete items from folders, outlook doesn’t seem to refresh the item list.  If you try and delete the item again, outlook throws an “unknown error” message.  If you delete an item and then navigate away from a folder or even use the navigation pane to display the same folder, the item list will refresh and remove the deleted message.

The issue is “The basic issue is that Outlook 2003 support UDP and polling notifications. Exchange 2007 supports UDP, polling and Async notifications. Exchange 2010 only supports polling and Async notifications. This means when Outlook 2003 move from Exchange 2007 to Exchange 2010, Outlook clients will fall back to polling which by default only gets notifications every 30secs-1min. This means any change won’t show up immediately.

UDP notification support was removed from Exchange 2010. As a result, Outlook 2003 can only use polling notifications in online mode, which are still supported by RPC Client Access. This will result in a slight delay in updates to item status (30 seconds on average up to a 1 minute delay) when changes are made to items in a mailbox accessed by Outlook 2003.”

The fix:

Method 1: Install Update Rollup 1 for Exchange Server 2010

Important This method contains steps that tell you how to modify the registry. However, serious problems may occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For more protection, back up the registry before you modify it so that you can restore the registry if a problem occurs. For more information about how to back up and then restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows

You can download Update Rollup 1 for Exchange Server 2010 from the following article in the Microsoft Knowledge Base:

976573 Description of Update Rollup 1 for Exchange Server 2010

After you install the update, you must add the following registry data to the server by using the Client Access role.

  1. Start Registry Editor.  
  2. Locate and then click to select the following registry subkey: HKEY_LOCAL_MACHINESystemCurrentControlSetServicesMSExchangeRPCParametersSystem Create the ParametersSystem


    registry subkey if it does not exist.

  3. Add the following registry data to the server:Value type: REG_DWORD
    Value name: Maximum Polling Frequency
    Value data: any integer between 5000 and 120000 (decimal value)

  4. Exit Registry Editor.


  • The registry change is dynamically detected. Therefore, the new settings will be applied to any new connections that clients make after the change is made. If you want to make sure that the new settings are applied to all clients, you should recycle the Microsoft Exchange RPC Client Access service because connections from clients can remain alive for a long time.
  • Outlook 2003 does not poll the Exchange Server 2010 server in intervals that are less than 10 seconds. Therefore, any value less than 10000 will generally have the same effect.
  • This change does not reinstate UDP communication between Exchange Server 2010 and Outlook 2003. This change only enables polling to occur more frequently between Exchange Server 2010 and Outlook 2003.

Microsoft KB – link