Running an Exchange organization in mixed and native modes:

Running an Exchange organization in mixed and native modes:

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When an administrator plans to deploy Exchange Server 2003 in a network, an important consideration for him is to decide the operational mode in which the Exchange organization will operate. An Exchange Server 2003 organization can operate in either mixed or native mode. The concept of the mixed-mode and native-mode Exchange organizations is similar to the idea of mixed-mode and native-mode domains in Active Directory. In Exchange Server 2003, mixed and native modes can be selected only at the organizational level. Both the modes have several advantages and disadvantages. Native mode provides full Exchange Server 2003 functionality, whereas in mixed mode, Exchange Server 2003 functions with some restrictions. The utmost reason for running an Exchange Server 2003 organization in mixed mode is its interoperability with previous versions of Exchange. When operating in mixed mode, an Exchange Server 2003 organization can support Exchange Server 5.0, Exchange Server 5.5, Exchange 2000 Server, and Exchange Server 2003 installations. On the other hand, in native mode, the organization supports only Exchange 2000 Server and Exchange Server 2003.

When Exchange Server 2003 is installed on a server, the operational mode is by default set to mixed. Although the mixed-mode configuration offers interoperability between servers running Exchange Server 5.5 and Exchange Server 2003, it limits the capabilities of the latter. These limitations affect how administrative groups are used and managed. Before choosing an operation mode, an administrator must consider the compatibility issues and future administrative plans. If he wants to retain or add the previous versions in the existing organization, he must opt for mixed mode. When running in mixed mode, the Exchange organization provides the following benefits:

1. It ensures interoperability between servers running Exchange Server 2003 and Exchange Server 5.5.


2. Routing between Exchange Server 2003 and Exchange Server 5.5 is possible.


3. Both Exchange Server 5.5 and Exchange Server 2003 objects can be managed from Active Directory.


4. Mixed mode allows an administrator to install servers running Exchange Server 5.5 in future.


5. All the Exchange Server 5.5 directory service objects are replicated to Exchange Server 2003 and are displayed in the Exchange System Manager console.

With these benefits, there are some limitations as well. They are as follows:

1. Each administrative group can have only one functional routing group.


2. Mailboxes cannot be moved from a server in one administrative group to a server in another administrative group, thereby reducing the flexibility in managing them. They can be moved only between the servers that are in the same administrative group.


3. Administrative groups cannot be created independently of the routing groups, as they are mapped directly to sites. Although servers can be moved between routing groups, the members of all routing groups must belong to the same administrative group.

There are additional limitations when Exchange Server 2003 is installed on an Exchange 5.5 site. These limitations are as follows:

1. Exchange Server 5.5 does not support some System Manager commands. Therefore, these commands cannot be used to manipulate an Exchange Server 5.5 server that is a part of the Exchange organization running in mixed mode.


2. Exchange Server 5.5 system objects present read-only properties when viewed from Exchange System Manager. As a result, an administrator cannot edit these properties through Exchange System Manager.

Once an Exchange Server 2003 organization is converted to native mode, the organization cannot interoperate with servers running Exchange Server 5.5. In order to be converted from mixed to native mode, an Exchange organization must contain servers running Exchange 2000 Server or Exchange Server 2003, or both. An administrator should opt for converting to native mode in the following cases:

1. The Exchange organization does not have any server running Exchange Server 5.5.


2. There is no possibility of adding servers running Exchange Server 5.5 to the organization in future.


3. The Exchange organization will never require interoperability with servers running Exchange Server 5.5.


4. The Exchange organization does not use any connectors or gateway applications that run only on Exchange Server 5.5.

Converting to native mode is a one-way process. It means that if an Exchange organization is converted to native mode, it cannot be reverted in future. Native mode has the following advantages over mixed mode:

1. It provides greater flexibility to define administrative and routing groups.


2. Mailboxes can be moved between the servers in different administrative groups.


3. Administrative as well as routing groups can be configured independently of each other.


4. Query-based distribution groups can be created in an Exchange organization running in native mode.

An administrator can convert an Exchange Server 2003 organization from mixed to native mode through Exchange System Manager by right-clicking the organization name, clicking Properties, and clicking the Change Mode button in the Operation mode section. However, this button is unavailable if the organization is already running in native mode.

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