Consider the following scenario:
You have multiple Active Directory sites in a Microsoft Exchange Server 2010 environment that has Update Rollup 3 for Exchange Server 2010 Service Pack 2 or a later-version update rollup installed.
The Outlook Anywhere feature is enabled on the Client Access servers in each site.
You use Outlook Anywhere to connect to a mailbox through the Client Access server that is located in the same site as the mailbox.
You try to open another mailbox that is located in a different site and that you have sufficient permissions to access. For example, you try to open a shared mailbox that is located in a different site.
In this scenario, the operation fails and you receive an error message that resembles the following:
Cannot display the folder. Microsoft Outlook cannot access the specified folder location. The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
Additionally, the following event is logged in the RPC Client Access log on the Client Access server:
RopHandler: Logon: [RopExecutionException] The client should use Outlook Anywhere and RpcClientAccess server from site SiteName to access the mailbox.
To resolve this issue, install the following update rollup:
2803727 Description of Update Rollup 1 for Exchange Server 2010 Service Pack 3
To work around this issue, apply the following setting on all internet-facing Client Access servers:
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\MSExchangeRPC\ParametersSystem
On the Edit menu, point to New, and then click DWORD (32-bit) Value.
Type EnablePreferredSiteEnforcement, and then press Enter.
In the Details pane, right-click EnablePreferredSiteEnforcement, 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 issue, click the following article numbers to view the articles in the Microsoft Knowledge Base:
2685289 Description of Update Rollup 3 for Exchange Server 2010 Service Pack 2
2725008 Outlook Anywhere clients cannot connect to a CAS server after you apply Exchange Server 2010 SP2 RU3