Understanding Mixed and Native Modes


Exchange Server 2003 is always installed in mixed mode which allows it to coexist with Exchange 5.5. In mixed mode, some Exchange 2003 features are not available. In order to enable these features, Exchange must be run in what is called native mode. However, once you move to native mode you cannot switch back to mixed mode. In other words, once you are in native mode you can no longer have Exchange 5.5 servers coexist in the same organization.

Because some Exchange 2003 features are available only when you run in native mode, it is recommended that you switch from mixed mode to native mode as soon as feasible.


There is no direct relationship between the mode of the Microsoft Windows® domain and the mode of an Exchange organization. The similarity exists only in terms of naming and restrictions on earlier versions.

This topic will discuss the advantages of native mode and help you decide if you are ready to move to native mode.

Features available in mixed mode vs. native mode

Feature Available in mixed Exchange 5.5, Exchange 2000, and Exchange 2003 organization? Available in Exchange 2003 or Exchange 2000 native mode? Available in pure Exchange 2003 organization that is in native mode?

Move mailboxes between servers in the same administrative group




Move mailboxes between servers in different administrative groups




Create an administrative group that spans multiple routing groups




Use query-based distribution groups




InetOrgPerson object can be mail-enabled or mailbox-enabled




Running in Mixed Mode

For Exchange 5.5, Exchange 2000, and Exchange 2003 to coexist and replicate directory information, the Exchange 2000 and Exchange 2003 configuration must remain in a state that Exchange 5.5 can recognize. Running your Exchange organization in mixed mode allows for interoperability among these versions of Exchange. ADC is also critical to ensure coexistence between the Exchange 5.5 directory and Active Directory.


Because of the limitations of mixed-mode operation, you should not operate in mixed mode if your organization uses strictly Exchange 2000 and Exchange 2003 servers and if you are sure you will not install an Exchange 5.5 server into your organization.

Mixed mode is designed only for interoperability between Exchange 2003 servers and Exchange 5.5 servers, and you should plan to switch to native mode as soon as it is feasible. Operating your Exchange organization in mixed mode has the following limitations and issues:

  • Exchange 5.5 sites map directly to administrative groups and vice versa.

  • You can only move mailboxes between servers that are in the same administrative group.

  • You cannot move Exchange 2003 servers between routing groups

  • Routing group membership must consist only of servers installed in the administrative group that is defined with the routing group.


    When an Exchange 2003 organization is in mixed mode and Exchange 5.5 sites are mapped one-to-one with administrative groups, you can subdivide the routing structure for the Exchange 2003 servers in the collection by using routing groups. Because in mixed mode a particular routing group can belong to only one administrative group, a server cannot belong to a routing group that is held under a different administrative group. Exchange 5.5 servers do not make these routing group distinctions and continue to use the site boundary for routing purposes.

Advantages of Running in Native Mode

Running an Exchange organization in native mode gives you the full flexibility of Exchange 2003 when you manage your messaging system.

Running Exchange 2003 in native mode has the following advantages:

  • Distribution groups can be created dynamically. In Native mode   you can create query-based distribution groups. A query-based distribution group provides the same functionality as a standard distribution group. However, instead of specifying static user memberships, with a query-based distribution group you can use an LDAP query to build membership in the distribution group dynamically. For more information about query-based distribution groups, see "Managing Recipients and Recipient Policies in Exchange Server 2003" in the Exchange Server 2003 Administration Guide.

  • Native mode saves bandwidth   Your routing bridgehead server pairs use 8BITMIME data transfers instead of converting down to 7-bit. This equates to a considerable bandwidth saving over routing group connectors.

  • Administrative groups can be renamed.

  • Consolidate administrative groups and define routing groups and administrative groups with greater flexibility.

  • Routing groups can consist of servers from multiple administrative groups.

  • You can move Exchange 2003 servers between routing groups.

  • Move mailboxes between servers in different administrative groups.

  • You no longer have to maintain ADC and Site Replication Service.

  • Simple Mail Transfer Protocol (SMTP) is the default routing protocol.

  • **Support for InetOrgPerson   **The InetOrgPerson object class is used in several non-Microsoft LDAP and X.500 directory services to represent people within an organization. Exchange 2003 supports InetOrgPerson to make migrations from other LDAP directories to Active Directory more efficient. You can create an InetOrgPerson only if you are running a Windows Server 2003 domain controller. InetOrgPerson can be mail-enabled or mailbox-enabled only when the organization is a pure Exchange 2003 organization running in native mode.

  • The Exchange store in Exchange 2003 ignores and removes zombie access control entries (ACEs) from the previous Exchange 5.5 servers in your organization automatically. These zombie access control entries are security identifiers from previous Exchange 5.5 servers that have been removed from your organization.

What mode are you in?

If you are not sure which mode you are currently running in, see "How to Determine if You Are Running Exchange in Mixed or Native Mode."

Are you a candidate for switching to Native Mode?

You can change your Exchange 2003 organization to native mode if:

  • You no longer have Exchange 5.5 servers in your organization.

  • You have no plans to add Exchange 5.5 servers to your organization in the future, for example, as a result of a merger or the acquisition of a company with Exchange 5.5 servers.

  • Your company will never require interoperability between your Exchange 2003 or Exchange 2000 servers and Exchange 5.5. (You can use connectors to provide connectivity to older versions of Exchange; however, these servers exist outside the Exchange organization.)

  • Your organization does not use any connectors or gateway applications that run only on Exchange 5.5.

After you switch your Exchange 2003 organization from mixed mode to native mode, you cannot switch the organization back to mixed mode. Make sure that your Exchange 2003 organization will not have to interoperate with Exchange 5.5 in the future before you switch to native mode.

Preparing to Switch to Native Mode

Before you switch to native mode you must remove any Exchange 5.5 servers in your organization and remove the Site Replication Service (SRS).


If you did not install Exchange 2003 into an Exchange 5.5 organization, you do not need to perform these two steps. See "How to Switch to Native Mode."

Remove Exchange 5.5 Servers

Before you can switch from mixed mode to native mode, you must remove all Exchange 5.5 servers in your organization. See "How to Remove Exchange 5.5 Servers from Your Exchange 2003 Organization."

Remove Site Replication Service

Site Replication Service (SRS) is a component that exchanges configuration information between Active Directory and the directory in Exchange 5.5. By default, SRS is installed on the first Exchange server you installed in an Exchange 5.5 organization. However you can move SRS if the initial server installed needs to be removed from the organization such as in the case of a hardware failure. SRS is necessary because without SRS Exchange 5.5 configuration information can only be shared with Exchange 5.5 servers and Exchange 5.5 directories—not with Active Directory. SRS mimics an Exchange 5.5 directory so that other Exchange 5.5 servers can replicate information to Active Directory through SRS. Using the configuration connection agreement created by Exchange Setup, Active Directory Connector replicates the configuration information in SRS into Active Directory.

SRS runs only in a mixed-mode Exchange administrative group. SRS also performs additional functions, such as detecting and reacting to directory replication topology changes. You cannot switch from mixed mode to native mode until you have removed all instances of SRS.

SRS is enabled automatically in two situations:

  • On the first Exchange 2003 server you install in an Exchange 5.5 organization.

  • When you upgrade to Exchange 2000 from an Exchange 5.5 server that is the directory replication bridgehead server for an organization.

See "How to Remove Exchange SRS."

Switching to Native Mode

When you are sure that your Exchange 2003 organization will not have to interoperate with Exchange 5.5 in the future and you have removed any Exchange 5.5 servers and the SRS service, you can switch to native mode. See "How to Switch to Native Mode."

For More Information

For more information, see "How to Switch to Native Mode."