How to Set the MDB Users Registry Value

  • Article

 

The MDB users registry value is the maximum number of MDB users who are supported by the MTA. All Exchange Server users are MDB users by default unless they are explicitly set otherwise. MDB users defines the number of distinguished names (DNs) 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.

In smaller organizations, the MTA process typically does not require manual tuning. After you have converted to Native Mode, you should remove these registry settings. Using the MTA tuning described below in a Native Mode Exchange organization decreases the performance of Exchange.

Before You Begin

Before you perform the procedure in this topic, be aware that the procedure contains information about editing the registry.

Warning

Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

Procedure

To set the MDB users registry value

  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 MDB users.

  4. In the Value data field, enter the appropriate value for your organization and click OK.

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

For More Information

For information about how to edit the registry, see Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=256986).