Description of mixed mode and native mode in Exchange 2000 Server and in Exchange Server 2003

A Microsoft Exchange 2000 Server or Microsoft Exchange Server 2003 organization runs in one of two modes of operation: mixed mode or native mode. This article describes the differences between mixed mode and native mode.

Mixed mode

An organization that is running in mixed mode can handle all versions of Exchange Server. By default, Exchange 2000 Server and Exchange Server 2003 are installed in mixed mode.

Mixed mode organizations have the following characteristics:

• Different versions of Exchange Server can coexist in the same organization.
• Functionality is limited to features that are shared by versions of Exchange Server that exist in the organization.
• Rules that apply to earlier versions of Exchange Server also apply to later versions, even though those limitations may not exist in the later version.

When you introduce an Exchange 2000 Server or Exchange Server 2003 computer into an existing Microsoft Exchange Server 5.5 Service Pack 3 (SP3) or later site by using the installation process, Site Replication Service (SRS) and Active Directory Connector (ADC) are installed. If you upgrade an existing Exchange Server 5.5 computer to Exchange 2000 Server or to Exchange Server 2003, you must install ADC before you upgrade. However, SRS is automatically installed. These components work together to provide remote procedure call (RPC) replication in a site and mail-based replication among sites. ADC Connection Agreements between Active Directory and the SRS database are automatically established to enable directory replication.

To other Microsoft Exchange Server 4.0, 5.0, and 5.5 computers in the site, the Exchange 2000 Server or Exchange Server 2003 computer appears as just another server. The servers send out directory replication notifications as usual. Also, the SRS database requests changes just like earlier versions of Exchange Server request changes.

Mixed mode exists to maintain backward compatibility. However, mixed mode limits the system to the constraints that are imposed by earlier software releases. In a mixed mode site, the rules that apply to earlier versions of Exchange Server also apply to Exchange 2000 Server or Exchange Server 2003.

The following limitations apply to Exchange 2000 Server or to Exchange Server 2003 in a mixed-mode environment:

• Exchange Server 5.0 and 5.5 sites are mapped directly to administrative groups.
• Administrative groups are mapped directly to Exchange Server 5.0 and 5.5 sites.
• Routing group membership consists only of servers that are installed in the administrative groups.

Native mode

An organization that is running in native mode can contain only Exchange 2000 Server or later computers. New Exchange Server 5.0 or 5.5 computers cannot be introduced into the organization.

When you have a configuration with Windows 2000 domain controllers and global catalog servers on the local network, these servers must have Windows 2000 Server SP3 or later installed if the domain controllers and global catalog servers will communicate with the Exchange Server computer or with Active Directory Connector (ADC).

You can change an Exchange 2000 Server or Exchange Server 2003 organization to native mode after all the servers are upgraded to Exchange 2000 Server or to Exchange Server 2003 and if earlier release restrictions no longer apply. You cannot switch to native mode until you either upgrade or decommission all earlier versions of Exchange Server.

The following are some of the features of Exchange 2000 Server or Exchange Server 2003 native mode:

• Routing groups can consist of servers from multiple administrative groups.
• Servers can be moved between routing groups.
• Simple Mail Transfer Protocol (SMTP) is the default routing protocol.
• Lightweight Directory Access Protocol (LDAP) queries can be used to create dynamic query-based distribution groups.
• Routing bridgehead server pairs use 8BITMIME data transfers to provide significant bandwidth improvement over routing group connectors.
• The Information Store service in Exchange Server 2003 automatically ignores and removes "zombie" Access Control Entries (ACEs) from the Exchange Server 5.5 computers that were previously used in an organization.
• Mailboxes can be moved across administrative groups.
• The InetOrgPerson object class can be mailbox-enabled or mail-enabled.
  
  Note Servers cannot be moved between administrative groups in either mixed mode or in native mode.

How to determine the mode in which the Exchange Server organization is running

By default, an Exchange 2000 Server or Exchange Server 2003 organization runs in mixed mode. To determine the mode in which the Exchange 2000 Server or Exchange Server 2003 organization is currently running, follow these steps:

1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Right-click the organization for which you want to determine the mode, and then click Properties.
3. Click the General tab. Under Operations Mode, the operating mode of the organization is displayed.

How to change modes

Note Before you can change an organization from mixed mode to native mode, all of the computers in the organization must be running Exchange 2000 Server or Exchange Server 2003. Before you can upgrade computers that are running Exchange Server 4.0 or 5.0 to Exchange 2000 Server or Exchange Server 2003, you must upgrade these computers to Exchange Server 5.5 Service Pack 3. Exchange Server 4.0 and 5.0 cannot be upgraded directly to Exchange 2000 Server or Exchange Server 2003.

Important After you change to native mode, you cannot change back to mixed mode. This conversion is a one-time conversion. You must fully understand the results before you continue with the conversion.

After you upgrade or remove all versions of Exchange Server that are earlier than Exchange 2000 Server, you can switch the Exchange 2000 Server or Exchange Server 2003 organization to native mode by using Exchange System Manager:

1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Right-click the organization, and then click Properties.
3. Click the General tab, and then click Change Mode under Change Operations Mode.
4. Click Yes if you are sure that you want to permanently switch the organization's mode to native mode.

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
For more information about switching an Exchange organization to native mode, click the following article number to view the article in the Microsoft Knowledge Base:
For more information about UDG users cannot access PF in a mixed-mode Exchange 2000 or Exchange 2003 environment, click the following article number to view the article in the Microsoft Knowledge Base: