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This article discusses remote procedure call (RPC) protocol registry keys and how they can affect Microsoft Outlook connectivity to Microsoft Exchange Server. This article also discusses basic troubleshooting procedures.
Outlook uses RPCs to make calls to the network. RPCs permit Outlook to send calls to many different protocol stacks. The calls depend on the protocol stack that is available on the computer. The most common protocol is TCP/IP. Other RPC protocols include NetBIOS, NetBIOS over TCP/IP, and IPX/SPX. If a client computer sends the appropriate RPC protocol requests, the server must have those protocols available.
RPC protocol registry entriesThis section describes the main registry entries that control the RPC protocol that Outlook uses.
RPC_Binding_OrderThe RPC_Binding_Order entry is created when you install the Outlook client or Exchange Server. The RPC_Binding_Order entry determines the protocol sequence that is used when Outlook RPC communications are initiated.
Note The RPC_Binding_Order entry is not created in Microsoft Exchange Server 2003 or in Microsoft Exchange 2000 Server. This entry is only created in Microsoft Exchange Server 5.5 and in earlier versions of Exchange.
You can find this entry in the following registry key:
By default, the Rpc_Binding_Order entry contains the following value data:
ncalrpc,ncacn_ip_tcp,ncacn_spx,ncacn_np,netbios,ncacn_vns_sppFor more information about how to modify or restore the binding order, click the following article number to view the article in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/163576/ )Changing the RPC binding order
RPC_Srv_Binding_OrderThe RPC_Svr_Binding_Order registry entry is created when you install the Outlook client or Exchange Server. Do not confuse this entry with the RPC_Binding_Order registry entry. This entry is not used with Outlook RPC connections. This entry determines the protocol sequence that is used for certain server-to-server communications. You can use the RPC Dump utility to determine the protocols that are available for the clients to use. For additional information about the RPC Dump utility, see the "Use RPC Dump to identify server RPC issues" section of this article.
You can find the RPC_Svr_Binding_Order entry in the following registry subkey:
By default, the Rpc_Svr_Binding_Order entry contains the following value data:
ncacn_ip_tcp,ncacn_spx,ncacn_vns_sppNote Other values may be present if additional protocols are installed.
ClientProtocolsregistry subkey is created when you install the operating system and the first network protocol. The
ClientProtocolsregistry subkey contains entries that determine the protocols that can be used by the client operating system to connect to Exchange Server. Outlook can determine the RPC protocol to send; this registry subkey determines if the operating system supports that protocol. You can find this subkey in the following registry key on Microsoft Windows 2000 and Microsoft Windows XP:
By default, the
ClientProtocolssubkey contains the following registry entries for TCP/IP:
Note In Microsoft Windows NT 4.0, the registry subkey location is the same, but the default TCP/IP entries are different. The following table describes the default TCP/IP entries for Windows NT:
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Note In Microsoft Windows 98, the subkey is in the same location, but the default TCP/IP entries are different. The following table describes the default TCP/IP entries for Windows 98:
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Collapse this tableExpand this table
Troubleshoot RPC registry entriesIf one or more of the RPC registry entries are missing, Outlook may not connect to Exchange Server. If the
ClientProtocolssubkey or data values are missing, the Outlook client may not be able to use the expected protocol to connect. For Outlook to use the appropriate RPC protocol, the
ClientProtocolssubkey and data values must be present and accurate.
For example, on the computer that is running Outlook, if the only RPC ClientProtocols registry entry that is present is ncacn_np (with a value of rpcrt4.dll), Outlook tries to connect to the computer that is running Exchange Server by using named pipes over TCP/IP on the default port of 139. If the connection must traverse a firewall, port 139 must be open. The missing registry entry ncacn_ip_tcp (with a value of rpcrt4.dll) must be restored to support a TCP/IP connection that uses port 135 or port 445 to the Exchange Server.
Additionally, if the RPC registry entries are missing on the server, the Exchange services are not registered to respond to client requests. Therefore, the client cannot connect to Exchange by using the requested protocol. For example, if the server does not have the RPC ClientProtocols registry entry for ncacn_ip_tcp, the Microsoft Exchange Information Store is not available when you use TCP/IP to connect. You can use RPC Dump to troubleshoot this issue.
Outlook error messagesThe following error messages may appear in the Outlook client when the RPC registry entries are missing or corrupted:
Use Network Monitor to identify RPC issuesYou can use Network Monitor to identify RPC-related issues. For example:
Use RPC Dump to identify server RPC issuesYou can use the RPC Dump tool to troubleshoot server RPC issues. You can use the RPC Dump tool to list the RPC applications that are running on the server. There are three RPC components that must be available for the Outlook client to successfully connect:
The RPC Dump tool is typically used together with Network Monitor. For example, if the Outlook client cannot successfully verify a name, you can run the RPC Dump tool on the server that provides the NSPI.
Note If f5cc5a18-4264-101a-8c59-08002b2f8426 is missing from a global catalog server for TCP/IP (ncacn_ip_tcp), the Outlook clients cannot connect to the NSPI over TCP/IP.
You can also use the RPC Dump tool when Outlook clients can successfully verify the names, but the Outlook clients cannot log on to the mailbox. By running the RPC Dump tool, you can determine if the store (a4f1db00-ca47-1067-b31e-00dd010662da) is registered with RPC with TCP/IP (ncacn_ip_tcp), Named Pipes (ncacn_np), or other protocols. This problem is typically caused by missing
ClientProtocolsregistry entries on the server. The problem may also occur if both the NSPI and the store are statically mapped to the same port.
For more information about static port mappings for Exchange Server 2003 and Exchange 2000 Server, click the following article number to view the article in the Microsoft Knowledge Base:
270836Note The RPC Dump tool does not list the endpoint mapper. For additional information about how to obtain the RPC Dump tool, visit the following Microsoft Web site:
(https://support.microsoft.com/kb/270836/ )Exchange Server static port mappings
Restore missing RPC registry valuesTo restore missing RPC registry values on the client or on the server, follow these steps.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
Step 1: Verify registry entries
Step 2: Verify the version of the DLL fileIf all the registry values exist, verify the version of the RPC DLL file that is on the computer. The version of the RPC DLL file must match the version and the build number of the Windows operating system on the computer.
Note The registry keys that are described earlier in this article list the names of the .dll files that each RPC uses. For example, Rpc4rt4.dll is the .dll file that is used by TCP/IP on Windows 2000 and on Windows XP.
To determine the version and the build number of the Windows operating system on the computer, follow these steps.
Step 3: Remove and then reinstall TCP/IPImportant This step must only be performed on the client computer or computers.
On the Outlook client computer, if you cannot reestablish Exchange Server connectivity by following steps 1 and 2, remove and then reinstall TCP/IP. Microsoft recommends that you do not remove the TCP/IP protocol from the server. To remove and then reinstall TCP/IP on the client computer, follow these steps:
For more information about how to troubleshoot connectivity issues, click the following article numbers to view the articles in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/255843/ )Unable to log on to Exchange Server from a Windows 2000 or Windows XP client
(https://support.microsoft.com/kb/321652/ )You receive error message and are continuously prompted for your Windows NT domain credentials in Outlook 2000 or in Outlook 2002
(https://support.microsoft.com/kb/319517/ )You receive an error message when you use Outlook 2002 on Windows 2000 Terminal Services
(https://support.microsoft.com/kb/326036/ )Cannot log on to Exchange 2000 Server computer by using the correct credentials
(https://support.microsoft.com/kb/319572/ )Exchange 2000 Server cannot register Outlook new mail notifications
Article ID: 325930 - Last Review: September 3, 2013 - Revision: 7.0