Jemima mailed me with a question:
If I have a mixed mode Exchange 2003/5.5 environment of one site, can I install a second Exchange 2003 server into a new site? (and how) Or do I have to change to native mode to do so?
Chapter 6 of the Exchange Deployment guide details the following about mixed mode…
Switching from Mixed Mode to Native Mode
Because Exchange 2000 and Exchange 2003 are structured to take advantage of Active Directory functionality, there are some limitations when Exchange 2003 coexists in the same organization with Exchange 5.5. When Exchange 2000 or Exchange 2003 servers coexist with Exchange 5.5, your organization must run in mixed mode.
Running in mixed mode limits the functionality of Exchange 2003. Therefore, after migrating from Exchange 5.5 to Exchange 2003, it is recommended that you switch from mixed mode to native mode. This section discusses the advantages of a native-mode Exchange organization and provides the steps that are necessary to switch from mixed mode to native mode.
You are ready to change your Exchange 2003 organization to native mode if:
• Your organization will never require interoperability between your Exchange 2003 servers and Exchange 5.5 servers in the same organization.
• Your Exchange 5.5 servers exist in an organization that is separate from your Exchange 2003 servers.
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 from mixed mode to native mode.
First, however, you should determine in which mode your Exchange organization is currently running.
Jemima didn’t say whether she still needed to keep connectivity with the 5.5 servers or not. If not, then follow the steps in chapter 4 of the deployment guide
There are also some useful tips in Chapter 3 of the Planning an Exchange server messaging system To create a new site for Exchange read how we did it at Microsoft:
Hope this helps a little…