Topic Last Modified: 2007-01-08

The Microsoft® Exchange Server Analyzer Tool reads the following registry value to determine whether the polling interval for Microsoft Office Outlook® 2003 and Outlook 2007 clients that access Exchange Server 2003 or Exchange Server 2007 using RPC over HTTP has been modified from its default value:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\ Maximum Polling Frequency

If the Exchange Server Analyzer finds that the Maximum Polling Frequency key is present and configured with a value more than 0, a non-default configuration message is displayed.

When it makes its initial connection to an Exchange server, Outlook registers itself for new message notifications. Whenever a new message is received in an Outlook user’s mailbox, Exchange sends a notification to Outlook using User Datagram Protocol (UDP). When Outlook receives this notification, it retrieves the message from the Exchange server and displays it in the appropriate folder. If Outlook does not receive new mail notifications, it reverts to polling the Exchange server. Although polling is initiated by Outlook, polling frequency is dictated by the Exchange server.

By default, Outlook 2003 polls every 60 seconds. You can change the frequency by adding the Maximum Polling Frequency registry entry to the Exchange server that contains the user’s mailbox. The value you enter is the minimum number of milliseconds between polling intervals. If Maximum Polling Frequency is not present, a default value of 60 seconds (60,000 milliseconds) is used. This default value does not mean that polling occurs every 60 seconds. Rather, the value means that polling will occur any time between the polling frequency interval and two times that interval. For example, assume that Maximum Polling Frequency is set to 90 seconds. In that example, polling occurs between 90 and 180 seconds after the last poll.

You should not reduce the value below the default value of 60 seconds because doing this will degrade performance for Exchange, Outlook, and the network. You may not need to adjust this value because many user actions will check for new messages as part of internal operations. For example, if a user switches between folders or opens a message, new items on the server will be displayed. This outcome occurs because when Outlook sends necessary RPC requests to Exchange to effect the user action, the new message flag is checked and, if present, the new message notification is included in the RPC response sent back to Outlook.

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 revert to the default configuration

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

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem

  3. Delete the Maximum Polling Frequency registry value.

  4. 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 RPC over HTTP, see the Exchange Server 2003 RPC over HTTP Deployment Scenarios guide (