HOW TO: Use Expansion Servers in Exchange 2000

This step-by-step article describes how to configure Exchange 2000 to use predetermined expansion servers to send e-mail messages to some or all of the Microsoft Windows 2000 distribution lists in your company. However, you must consider the factors about expansion server configuration that this article describes and how those factors relate to your company's deployment scenario.

NOTE: For a complete description of Windows 2000 security and distribution groups, see the Exchange Up-to-Date article "The Role of Groups and Access Control Lists in Microsoft Exchange 2000 Server Deployment." To view the Exchange Up-to-Date article "The Role of Groups and Access Control Lists in Microsoft Exchange 2000 Server Deployment," visit the following Microsoft Web site: For information about how to configure a server running Exchange to act as the expansion server for a particular group, see the "Selecting the Server Used to Expand a Group" section of this article.

Understanding the Role of Expansion Servers

Expansion servers route messages that are sent to a single Microsoft Exchange Server version 5.5 distribution list or to a Windows 2000 group for each of the recipient objects in that group.

Because Windows 2000 groups are similar to Exchange Server 5.5 distribution lists, the Active Directory Connector (ADC) replicates Exchange Server 5.5 distribution lists to the Active Directory directory service as Windows 2000 groups.

NOTE: In this article, the term "group" refers to both Windows 2000 groups that are e-mail enabled and Exchange 5.5 distribution lists. A group represents a collection of recipient objects. A group expedites the distribution of messages and other information to multiple e-mail addresses. When a message is sent to a group that is e-mail enabled, each member of that group receives a copy of the message.

When a user in your organization sends a message to a group, the Exchange computer that acts as the expansion server expands the group to its individual members. This expansion permits members to receive the message. The expansion server also resolves the names of all recipients in the group, and then determines the most efficient message routing.

NOTE: The default expansion server for a Windows 2000 group can be any server in the organization. Any server in the Exchange organization can function as an expansion server.

Expansion Server Configuration Scenarios

The most efficient method to expand recipient objects in groups that are e-mail enabled depends on your topology and other factors. The following sections describe specific deployment scenarios.

Exchange Deployments That Include the ADC but Do Not Include Exchange 2000

This deployment scenario does not involve Exchange 2000 and is known as a pure ADC deployment. In this scenario, the ADC replicates information between Exchange Server 5.5 and Active Directory. Important points to consider about expansion servers and Exchange Server 5.5 sites in this deployment are:

�	Groups are associated with an Exchange Server 5.5 site as soon as they are replicated from Active Directory to the Exchange Server 5.5 directory.
�	You cannot set the expansion server in Active Directory Users and Computers until the group is replicated to the Exchange Server 5.5 directory.
�	You can specify an expansion server that is in the same site as the distribution group object.

Exchange Server 5.5 and Exchange 2000 Mixed-Mode Deployments

This deployment scenario involves an Exchange organization that includes Exchange Server 5.5 and Exchange 2000.

In this deployment, consider the roles of expansion servers, Exchange Server 5.5 sites, and administrative groups:

�	When you create a group, specify an administrative group that you want to associate the group with.
�	Specify an expansion server that is located in the same Exchange Server 5.5 site or administrative group as the group object.

Exchange 2000 Native-Mode Deployments

This deployment scenario involves an Exchange organization that deploys Exchange 2000.

NOTE: If your Exchange organization is still in mixed mode, you cannot take advantage of the native-mode expansion server configuration options. You must first set your Exchange organization to native mode.

In this deployment, consider the roles of expansion servers and administrative groups:

�	You can set expansion servers to any server in any administrative group.
�	When you create a distribution group, it is associated with the default administrative group.

NOTE: The default administrative group is identified by the msExchDefaultAdminGroup attribute of the msExchAdminGroup object. There is no user interface that you can use to change this value. The default administrative group is the first administrative group that you create in your Exchange organization. If the default administrative group is deleted, Exchange makes the first administrative group that it finds the default administrative group.

Considerations for Configuring an Expansion Server

If you do not designate a specific server as the expansion server that expands a message that is sent to a group, the first server that the message is submitted to expands the group, and then sends the message to all of the destination servers. The message is routed to all members who follow the routing configuration that you designated.

If you designate an expansion server, you can minimize message routing in your Exchange organization, which avoids taxing system resources. For example, if your distribution group's members are all on one server, you can designate the server that contains those members as the expansion server. Also avoid designating an expansion server if your distribution groups are not aligned geographically.

Generally, designate an expansion server for a group when:

�	Users from the whole organization send e-mail messages to the group.
�	The group members are centrally located.

NOTE: There is a drawback to setting a specific server as the expansion server for a group. If that server is down, no members of the distribution group receive the message. However, if you leave the default Any Server in the Organization setting, most of the users receive their messages if one server does not work. Also, if all members of a distribution group are on well-connected servers, you do not have to set a specific expansion server.

Remember that the expansion process can be processor-intensive. If your Exchange organization is large and your distribution lists contain many members, a significant burden is placed on the Exchange message transfer agent (MTA) when messages are sent to Windows 2000 groups that are e-mail enabled and to Exchange Server 5.5 distribution lists. Therefore, Microsoft recommends that you isolate one server (perhaps a server that contains few or no user mailboxes) in the site or routing group that is responsible for all group expansion.

Selecting the Server Used to Expand a Group

You can select the expansion server that is used to expand a group that is e-mail enabled to a list of group members.

To select the expansion server:

1.	Click Start, point to Programs, point to Administrative Tools, and then click Active Directory Users and Computers.
2.	In Active Directory Users and Computers, click to select the Advanced Features check box on the View menu.
3.	Expand the console tree, click the group that you want to modify, and then double-click the group in the details pane.
4.	Click the Exchange Advanced tab, and then click the server that you want to use to expand the group in the Expansion Server list.

For additional information about Exchange in mixed mode and native mode, click the article number below to view the article in the Microsoft Knowledge Base: For additional information about when to change an Exchange organization to native mode, click the article number below to view the article in the Microsoft Knowledge Base: