XADM: How to Limit the Number of Messages Opened for Each MAPI Logon

A new feature in Exchange 2000 allows you to 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 inadvertently open very large numbers of messages, thereby affecting overall server performance. For additional information about the latest service pack for Microsoft Exchange 2000 Server, click the article number below to view the article in the Microsoft Knowledge Base:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value name: MaxOpenMessagesPerLogon
   Data type: REG_DWORD
   Data: 500 (set the type to Decimal)
   Set the Data value limit to the number of simultaneously open messages for each client logon that you want; 500 is recommended for most environments.
4. Quit Registry Editor.
5. Restart the Information Store service.

NOTE: With this setting in place, each client can open no more than 500 messages. Open attachments do not count against this restriction, but open free documents in the database are restricted along with messages.