Understanding the difference between mixed mode and native mode in Exchange 2000

Exchange 2000 has many new features, but you can't use them if Exchange 2000 is running in mixed mode. In this Daily Feature, John Sheesley explains mixed and native mode and how they relate to Exchange 2000.

As you probably know from working with Windows 2000, you can operate Windows 2000 in two different modes. First, there’s mixed mode, in which Windows NT and Windows 2000 servers and domain controllers can coexist. Second there’s native mode, which you use when you’ve completely converted all of your servers and workstations to Windows 2000. But did you know that Exchange 2000 also has native and mixed modes? In this Daily Feature, we’ll look at the differences between the two Exchange 2000 modes.
Even though Windows 2000 can run in mixed mode or native mode, those modes have nothing to do with mixed or native mode in Exchange 2000. Microsoft uses the same terminology, and the concepts of the two different modes are similar, but they have nothing to do with each other. For example, you could run Exchange 2000 in native mode while still operating the Windows 2000 server on which it’s running in mixed mode.
What’s mixed mode?
As you can probably guess by the name of the term, mixed mode in Exchange 2000 means that Exchange 2000 functions in a manner that allows it to work with other Exchange servers. Specifically, in mixed mode, Exchange 2000 can operate with Exchange 4.0, 5.0, or 5.5 servers, as well as other Exchange 2000 servers. When an Exchange 2000 server is working in mixed mode, it operates and communicates in a way that earlier versions of Exchange understand. To the other servers, the Exchange 2000 server is just another 4.x or 5.x server.

If you add an Exchange 2000 server to a network where there are already Exchange 4.x or 5.x servers, Exchange 2000’s Setup program installs the Site Replication Service (SRS) and Active Directory Connector (ADC) along with its other programs. When Exchange 4.x and 5.x send directory replication notifications across the network, the Exchange 2000 server uses the SRS and ADC to request information in a format compatible with those earlier versions.

As you know, Exchange 2000 does a lot more than earlier versions of Exchange did. When you run Exchange 2000 in mixed mode, it’s dumbed down so it can communicate with the earlier Exchange versions. In the process, Exchange 2000 loses some of its features. Exchange 2000 must play by Exchange 4.x and 5.x rules.

In mixed mode, you can’t move servers between administrative groups. Exchange 2000 administrative groups are tied to Exchange 5.x sites. Also, Exchange 2000 servers are forced to share service accounts with Exchange 4.x and 5.x servers. Finally, Exchange 2000 servers can only be included in routing group memberships if they exist in the shared administrative groups.

What’s native mode?
After you switch your Exchange 2000 servers to native mode, you’re no longer bound by the restrictions and limitations imposed by earlier versions of Exchange. You can create multiple routing groups, run SMTP as your native mail transport, move mailboxes between servers in the same administrative group, move servers from routing group to routing group, and build routing groups from multiple administrative groups.

Remember that when you run an Exchange 2000 server in native mode, it can no longer communicate directly with Exchange 4.x or 5.x servers. It can send and receive e-mail from them, but it can’t directly replicate changes or share stores. When you have Exchange 2000 servers running in native mode, you also can’t introduce any Exchange 4.x or 5.x servers into your network.

Going from mixed to native mode
If you have Exchange 4.x or 5.x servers in your organization, you can’t switch the mode of your Exchange 2000 servers to native mode until you either decommission or upgrade the 4.x and 5.x servers. Therefore, make sure you have no Exchange 4.x or 5.x servers left in your organization and no plans to add any 4.x or 5.x servers in the future. Verify that you aren’t running any special gateways or connectors that only support Exchange 5.5. After you’ve made sure that you no longer need operability with earlier versions of Exchange, you can switch modes.

When you first install Exchange 2000, Exchange 2000’s Setup program sets it to mixed mode—whether or not there are any Exchange 4.x or 5.x servers on your network. Even if your Exchange 2000 is brand new and is the only Exchange server on your network, Setup forces it to be in mixed mode.

To see which mode your Exchange 2000 server is currently running in, check the server’s properties in System Manager by clicking Start | Microsoft Exchange | System Manager. When System Manager starts, right-click the Organization object in the left pane and select Properties. Check the Operation Mode field on the General tab of the organization’s property page. The Operation Mode field displays the mode your server is currently running in.

If you want to change to native mode, click the Change Mode button on the General tab. Be very, very sure you want to change Exchange 2000’s mode. Once you switch to native mode, there’s no going back. (To switch back to mixed mode, your only choice is to reinstall Windows 2000 and Exchange 2000 on your server. When you click Change Mode, System Manager will display a warning screen reminding you of this fact.) Click Yes to complete the conversion.

In order to maintain backward compatibility with earlier versions of Exchange, Microsoft allows Exchange 2000 to run in one of two modes: mixed or native. If you’re running mixed mode, you’re missing out on some of Exchange 2000’s new features and advantages. In this Daily Feature, I’ve shown you the difference between mixed and native mode and how to make the switch.
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