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Strategies for migrating to AD with Exchange 5.5 server

I am thinking of the following strategy for migrating to AD. Please comment on its feasibility. We have a single NT domain with an Exchange 5.5 server. I was thinking of two scenarios:

1) Set up a separate AD domain and Exchange 2000 server. Is it possible to setup a one-way trust relationship between the NT and AD domains? Is it possible to synchronize the Exchange 5.5 and 2000 servers across the two domains? I'm thinking that to sync Exchange servers they have to belong to the same site, but if I build the Exchange 2000 and give it the same site name as the Exchange 5.5 would the sync work or do I have to establish the trust relationship first then join the Exchange 2000 to the Exchange 5.5 site? I want to maintain parallel domains so that if there are any major AD problems several months down the line I can revert to the old NT domain and still get an up to date e-mail server.

2) The second scenario is to not maintain parallel domains. My concern is that if we have to roll back to the NT domain after spending a few months running the Exchange 2000 server I will not be able to rebuild the Exchange 5.5 using the Exchange 2000 databases. I've rebuilt an Exchange 5.5 server using just a backup of the Exchange 5.5 dir.edb, priv.edb and pub.edb databases before, but knowing that Exchange 2000 does not have its own directory database but rather uses the AD as its directory source, I don't think I can rebuild the Exchange 5.5 using the Exchange 2000 data. Or am I wrong about that?

This is definitely a test network, but I just want to get some opinions and insights before I dive into setting up a test network and find out that it's not possible.

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: In my humble opinion, I think your second option is the best way to go. You mention that you have concerns about something going wrong with AD or experiencing major AD problems, forcing you to roll back to NT4/Exchange 5.5. To begin with, I have yet to encounter or hear of any organization that moved from NT4/Exchange 5.5 to AD/Exchange 2000 and had to roll back because of problems with AD (or with Exchange for that matter). I'm not saying this has never happened, just that I have never heard of it.

Given that Active Directory has been around for several years now, and given that much of it is based on the Exchange 5.5 directory, you can consider it a fairly mature directory and directory service. With more than three years of real-world deployments under its belt, Microsoft has learned a lot and improved Active Directory since its first release.

What you really want to do is spend a lot of time planning your AD/Exchange 2000 rollout and doing lots of hands-on testing in a lab environment. You'll want to build this infrastructure in such a way so that if you do have an AD or Exchange problem, you can fix the problem (or recover from it) and not have to scorch the Earth and rollback to NT/Exchange 5.5. There are plenty of ways to mitigate your risks that are better than a new forest/Exchange org.

This was first published in November 2003

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