Topic Last Modified: 2007-05-14

The Microsoft Exchange Analyzer Tool reads the following registry entry to determine whether the MaxOpenMessagesPerLogon registry value is present and configured:


If the Exchange Analyzer finds the MaxOpenMessagesPerLogon registry value present and configured to have a value more than 0, a nondefault configuration message is displayed.

Every time that a MAPI client or application opens a message on an Exchange Server computer, it causes the Microsoft Exchange Information Store service (store.exe) to consume a small amount of physical memory. When the message is closed by the Microsoft Office Outlook 2003 or Outlook 2007 clients, the memory is released. To prevent one or more MAPI clients from causing the Exchange store service to continuously allocate memory, a new configuration feature was introduced in Exchange 2000 Server Service Pack 1 (SP1) that lets an administrator limit the number of messages each MAPI client logon session can open simultaneously. Setting such a limit may be useful in your environment if certain client applications unintentionally open many messages, thereby affecting overall server performance.

This feature is implemented by using the MaxOpenMessagesPerLogon registry value on the Exchange Server computer. We recommend that a limit no more than 1000 be set. A value of 1,000 allows each client to use approximately 4 to 6 megabytes (MBs) of memory. For some environments, a smaller value of 500 may be more appropriate.

This article contains information about how to edit the registry. Before you edit the registry, make sure that you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To configure a maximum number of simultaneously opened messages

  1. Open a registry editor, such a Regedit.exe or Regedt32.exe.

  2. Open:


  3. Right-click ParametersSystem, select New | DWORD Value, and give the new value a name of MaxOpenMessagesPerLogon.

  4. In the right pane, double-click the MaxOpenMessagesPerLogon value, and then enter the maximum number of simultaneously open messages, in decimal.

  5. Close the registry editor and restart the Microsoft Exchange Information Store service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (

For more information about the MaxOpenMessagesPerLogon registry value, see Microsoft Knowledge Base article 289109, "XADM: How to Limit the Number of Messages Opened for Each MAPI Logon" (