In Exchange 2007, Outlook and other MAPI clients communicated with the Client Access server for HTTPS connections such as Exchange Web Services (including the Availability service and Out of Office settings), and Offline Address Book downloads, but communicated directly with the MAPI RPC component on the Mailbox server and the NSPI endpoint on Global Catalog servers for Directory Service inquiries.

In Exchange 2010, these connections are made to the MAPI RPC connection point on the Client Access server or the Client Access server array.

In previous versions of Exchange, DSProxy, a referral service that told Outlook clients where to find the Name Service Provider Interface (NSPI) endpoint, was responsible for directing Outlook to a global catalog server. DSProxy was located on the Mailbox server. DSProxy has been eliminated in Exchange 2010 and replaced with the Address Book service.

Currently, when an Outlook client makes a request of the Client Access server, it results in one of two possible actions.

• If the user's mailbox is on an Exchange 2010 Mailbox server, then either the request is handled by a Client Access server in the current Active Directory site, or if the user’s mailbox is in a different Active Directory site, the request is proxied to the destination Active Directory site.
  
  
• If the user's mailbox is on a legacy Exchange Mailbox server, the directory request is referred to the user's Mailbox server. Legacy Mailbox servers can't communicate directly with Exchange 2010 Client Access servers for directory information.
  
  

The Address Book service also provides information about writable domain controllers as well as global address list access. For more information about the Address Book service, see Understanding the Address Book Service.

You can create a Client Access array within your Active Directory site by using the following command.

	Copy Code
New-ClientAccessArray -Name name -Site site_name -FQDN internal_only_CAS_Array_FQDN

Note:
After the Client Access array has been created, you'll also need to create the address in DNS and associate it with the virtual IP address used for the Client Access array.

It's important that the (FQDN) specified in the command be only resolvable internally. If the name is also resolvable externally, these external clients will attempt to connect to the array via a TCP connection instead of HTTPS.

Load balancing is recommended for high availability, failover, and for spreading the traffic load over multiple servers to help performance. When you choose a load balancing solution, consider the following:

• Windows Network Load Balancing isn't supported on Windows failover cluster servers.
  
  
• You can't use a Client Access array across multiple Active Directory sites. Instead, create two Client Access arrays and load balance separately within the sites.
  
  
• Hardware load balancers typically monitor return traffic, port availability, or service availability to ensure that servers that can't answer client requests aren't given network connections.
  
  
• Some load balancing solutions, such as ISA 2006 or TMG 2010, can't do RPC load balancing or monitor RPC services. These solutions aren't recommended unless all clients are connecting via Outlook Anywhere and all traffic is encapsulated inside HTTP.
  
  

For more information about load balancing, see Understanding Load Balancing in Exchange 2010.

An IP port is an opening through which information can pass from the originating computer to the destination computer. By default, the dynamic port range for outgoing connections on Windows Server 2008 R2 is 49152 to 65535. Exchange 2010 Client Access changes this range to 6005 through 65535. The range was expanded to provide sufficient scaling for large deployments. This is a large range of ports to balance through your firewall between the client and the Client Access servers or Client Access array.

By fixing the MAPI and directory endpoints, you can greatly reduce the number of ports that need to be load balanced. The MAPI endpoint can be statically configured in the registry and the directory endpoint can be fixed in a configuration file.

To fix the MAPI endpoint, use the following setting in the registry.

HKLM\SYSTEM\CurrentControlSet\ Services\MSExchangeRPC\ParametersSystem\TCP/IP Port [DWORD] is the value for the IP port to use.

To fix the directory services endpoint, edit the RpcTcpPort value in the configuration file Microsoft.Exchange.AddressBook.Service.Exe.config.

Note:
We don't recommend that you change the default value of the Outlook Anywhere ports.

In the RTM version of Exchange 2010, the RPC endpoint is encrypted by default. However, Outlook 2003 doesn’t enforce encrypted MAPI connections. When you upgrade your organization to the RTM version of Exchange 2010, your clients running Outlook 2007 or later versions will automatically be compatible with the change to RPC Client Access, since they support RPC encryption by default. Outlook 2003 doesn’t use RPC encryption, however, and RPC Client Access requires it by default. If you haven't turned off RPC encryption, which we don’t recommend, your users will need to configure Outlook 2003 for RPC encryption or you'll need to use a Group Policy to force Outlook 2003 to use RPC encryption.

Symptoms of this problem include the following error messages:

• Cannot start Microsoft Office Outlook. Unable to open the Office window. The set of folders could not be opened.
  
  
• Unable to open your default e-mail folders. The information store could not be opened.
  
  

If your users are using Cached Exchange Mode, Office won't display an error, but will start in disconnected mode.

By default, Exchange 2010 Service Pack 1 (SP1) doesn't encrypt the RPC endpoint. If you've completed the installation of Exchange 2010 SP1 in your organization, Outlook 2003 clients will be able to connect to the Exchange server without further configuration.

For more information about this issue, including workarounds, see Outlook Connection Issues with Exchange 2010 Mailboxes.

Configure Outlook 2003 to Use RPC Encryption

Each Mailbox database contains an RPCClientAccessServer value. This value is established when the database is created and it determines the Client Access server or Client Access array that the clients with mailboxes on that Mailbox server will use. This value also determines the location of the RPC end point. For Outlook 2007 and Outlook 2010 clients, this value is obtained from the Autodiscover service.

The default value of the RPCClientAccessServer is determined by the following rules:

• If you have configured a Client Access Server array within your Active Directory site, the address of that array will be used.
  
  
• If an array does not exist within the Active Directory site and if you have both the Client Access server role and the Mailbox server role on the same physical server, the value of RPCClientAccessServer property for a particular Mailbox server will be the same as the Mailbox server.
  
  
• Otherwise, the value of the RPCClientAccessServer property for a particular Mailbox server will be set to a random Client Access server within the Active Directory site.
  
  

  Note:
  We don't recommend that you install all the server roles on a single computer that's also a domain controller. Although this configuration is supported, it's not recommended.

• If you created a Mailbox database before the creation of a Client Access array or the installed a Client Access server within the Active Directory site, you’ll need to reconfigure the value of the RPCClientAccessServer property. If no Client Access server exists in the Active Directory site when the Mailbox database is created, the value of the RPCClientAccessServer property will be set to the FQDN of the Mailbox server. To configure the value of the RPCClientAccessServer property, use the following command.
  
  

  	Copy Code
  Set-MailboxDatabase <name> -RPCClientAccessServer <internal_only_CAS_Array_FQDN>

For users running Outlook without Cached Exchange Mode, high latency times between the client and the server directly affect how frequently Outlook is unresponsive. In general, a latency of greater than 200 milliseconds (ms) to the home Mailbox server will result in poor client performance.

Because latency between the Client Access server and the mailbox should be less than 10 ms, we recommend that the value of the RPCClientAccessServer property always be configured to a Client Access array in the active Mailbox database site.

Note:
Changing the value of the RPCClientAccessServer property will force all clients to reconnect.

The Address Book service is configured through the Microsoft.Exchange.AddressBook.Service.config file. This file allows you to configure the following:

• The number of concurrent connections per user (the default limit is 50).
  
  
• Disable or enable logging.
  
  
• The location, size, and retention period for the log files.
  
  

To enable logging, use the following value:

< add key="ProtocolLoggingEnabled" value="true" />