In Exchange 2007 SP1, for clients to connect by using Outlook Anywhere when the Client Access server is running on Windows Server 2008, TCP/IPv6 connectivity must be manually disabled on all Exchange servers that have the Client Access server role installed.

To resolve the issue, perform one of the following procedures on the Client Access server. The procedure you use depends on whether your topology is running the Client Access server role and Mailbox server role on the same Exchange server or on different Exchange servers.

To perform the following procedures, the account you use must be delegated the Exchange Organization Administrator role. For more information about permissions, delegating roles, and the rights that are required to administer Exchange 2007, see Permission Considerations. 

1. Under Network Connections, select the network adapter, and then click Properties.

2. In the properties window, click to clear the check box for Internet Protocol Version 6 (IPv6).

   Note:
   Clearing this check box causes the RPCProxy component on the Client Access server to use TCP/IPv4 to talk to the DSProxy component on the Mailbox server.

3. Click Start, and then click Run.

4. Type regedit in the Open box.

5. Using Registry Editor, locate the following registry key:

   HKEY_Local_Machine\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters

6. Right-click the Parameters key, click New, and then click DWORD (32-bit) Value. For the key, add the following values:

   Name: DisabledComponents

   Data: 0xFFFFFFFF

7. Restart the Client Access server.

The preceding procedure does not work for a single-server topology where the Client Access server role is running on the same Exchange server as the Mailbox server role. This is because the loopback interface (an interface that is used when communicating through TCP/IP to a process on the same computer) continues to use TCP/IPv6. In this case, you must perform the following steps to disable TCP/IPv6.

1. Open the hosts file located at %SystemRoot%\system32\drivers\etc\ by using an editor such as Notepad.

   Note:
   In this step, %SystemRoot% refers to the local hard disk where the Windows system files are located.

2. Search for the line that contains the term "localhost" by using the CTR+F key combination.

3. Type a number sign (#) at the beginning and end of the line to make the line a comment.

4. Press ENTER and, on the next line, type the following lines to provide the TCP/IPv4 address, hostname, and FQDN name for the Exchange server that is running both the Client Access and Mailbox server roles:

      <TCP/IPv4 address>   <host name of the computer>

      <TCP/IPv4 address>   <FQDN of the computer>

5. Click Save, and then close the file.

For more information about TCP/IPv6, see IPv6 Support in Exchange 2007 SP1 and SP2.