Assume that you are in a Microsoft Exchange Server 2010 environment that has more than 64 multirole servers, and these servers contain Microsoft Exchange Server 2013. You find a default application pool that only hosts Microsoft Outlook anywhere is unresponsive. Additionally, when you try to use Outlook or Outlook Web App, you cannot log on to it.
This issue occurs because there is a whitelist of Exchange Server 2010 Remote Procedure Calls (RPC) over HTTP servers in the default application pool. In this pool, the default maximum number of Client Access servers is 64 in a single site. However, your RPC over HTTP ValidPorts registry key includes Exchange Server 2013 servers. It means the total number of Exchange servers exceeds the registry limitation. Therefore, a leak happens in heap.
To resolve this issue, install the following update:
Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.
To work around this issue, follow these steps to manually set this registry key:
Click Start, click Run, type regedit in the Open box, and then click OK.
Locate and then select the following registry subkey:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MSExchangeServiceHost\RpcHttpConfigurator\PeriodicPollingMinutes
Right-click the PeriodicPollingMinutes registry entry, and then click Modify.
In the Value data box, type 0, and then click OK.
Exit Registry Editor.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about the RPC over HTTP ValidPorts registry key, see Configuring Computers for RPC over HTTP.