Exchange operates in one of two modes — either "mixed mode" or "native mode." A mixed-mode configuration provides significant flexibility with interoperability between different versions of Exchange in your infrastructure. Mixed-mode Exchange domains can include Exchange 2003, 2000, 5.5 and 5.0, and even older, servers. A mixed-mode Exchange organization is used primarily to maintain backward compatibility with older Exchange servers. Bear in mind that if you are running in mixed-mode you are tied to the same limitations as Exchange 5.5 servers. All servers in the site need to use a common service account, and routing groups can only contains servers from one admin group.
If you have only Exchange 2000 and 2003 servers in your infrastructure, you can switch to native-mode, which offers some significant benefits over a mixed-mode configuration. First of all, SMTP (rather than RPC) is used as the default routing protocol. Second, you can use LDAP to create what Microsoft calls "query-based distribution groups." Third, services put into place—such as Active Directory Connectors—to support backward compatibility with older versions of Exchange can be removed, thus releasing some resources for your Exchange server to use. Other improvements, including the ability to move mailboxes between servers in the organization, and the ability to move servers between routing groups, are also a part of the native mode package. Under native mode, you can even rename your Exchange organization.
To upgrade your Exchange infrastructure to native mode, first understand that this is a permanent process. There is no undo.
- On an Exchange server, go to Start > All Programs > Microsoft Exchange > System Manager.
- Right-click your organization, and, from the resulting shortcut menu, choose the Properties option.
- Under the Change Operations Mode heading, click "Change Mode."
- Answer yes to the question.
No reboot is necessary to accomplish this goal.
You should know that the Active Directory mode has a bearing on how your Exchange infrastructure functions. If you're running a mixed-mode Active Directory (that is, you still have NT domain controllers), you won't be able to create Universal groups, which are an excellent way to build cross-domain mailing lists and so forth. In order to use Universal groups, you need to raise the functional level for your domain to Windows 2000 native or Windows 2003.