Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine its current value:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeMTA\Parameters\MDB users

If the Exchange Server Analyzer finds the value for MDB users present and set to anything other than 500, a non-default configuration message is displayed.

The MDB users value is the maximum number of message database (MDB) users who are supported by the message transfer agent (MTA). All Exchange Server users are MDB users by default unless they are explicitly set otherwise.

The MDB users registry value defines the number of distinguished names to cache from the directory. If your organization contains more than 1500 users, you should change the value to one-third the size of the global address list, but only to a maximum of 5000.

This article contains information about editing the registry. Before you edit the registry, make sure 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 correct this error

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

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeMTA\Parameters

  3. In the right pane, locate and double-click the MDB users value.

  4. In the Value data field, enter 500 and then click OK.

  5. Close the registry editor and then restart the Microsoft Exchange MTA Stacks 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" (