What to expect from Exchange 2010: Not much backward-compatibility

Brien Posey looks ahead to Exchange 2010 and what it means for your organization. Since Microsoft rebuilt it from the ground up, he expects the extremely limited backward compatibility to be a hurdle.

Although I have yet to see a definitive release date for Exchange 2010, Microsoft has provided us with a release candidate. That being the case, I think it makes sense for me to begin talking about Exchange 2010 and how it will fit in with your existing Exchange Server organization. Right now there are a lot of articles on the Internet discussing all the new features, so rather than rehashing Microsoft's marketing publications, I want to talk about what you can expect from the deployment process.


For me, one of the most surprising aspects of Exchange 2010 is its apparent lack of compatibility with previous versions of Exchange. I know that we can't stay stuck in the past and that technology constantly marches forward, but I have to admit that Exchange 2010's inability to interact with previous versions of Exchange caught me off guard.

The reason is that in the past, Microsoft has typically designed its new products to be backward-compatible with at least a couple of the previous versions. Granted, you can't always use all the new features until you get rid of the legacy versions, but at least the various versions can coexist until you complete your migration.

I'm not saying that Exchange 2010 offers absolutely no backward-compatibility; it does. It's just that Exchange 2010's backward-compatibility is extremely limited. To give you an idea of what I'm talking about, let me explain to you what happened when I installed the Exchange 2010 Release Candidate.

A few weeks ago, I finished recording a series of Exchange 2007 training videos. Prior to creating this video series, I had created a lab that I could use while developing the lessons in the videos. Being that the videos are finished, I decided to try to bring an Exchange 2010 Server into my existing lab environment rather than creating a brand-new forest and attempting to install Exchange 2010.

Prior to attempting an Exchange 2010 installation, my lab had several servers in it, including an Exchange 2003 mailbox server, an Exchange 2007 clustered mailbox server, a unified messaging server, an Exchange 2007 edge transport server, and another Exchange 2007 server that was hosting the client access server and hub transport server roles.

When I ran the Exchange 2010 prerequisite check, I received a message stating that coexistence with versions of Exchange 2007 SP2 is not supported. Without thinking, I moved all the mailboxes and public folders off my Exchange 2003 Server and decommissioned it. I attempted the installation again, and that is when it hit me that Exchange 2007 SP2 isn't even out yet!

Needless to say, I was not able to deploy Exchange 2010 into my existing lab environment. I was forced to set up a new forest prior to installing Exchange. What I found really interesting, though, is that if you are installing Exchange 2010 into a new organization, Exchange 2010 seems to install in native mode by default. The Setup Wizard actually told me that if I continued I would never be allowed to install Exchange 2007 servers in my organization.

In my opinion, the lack of compatibility with previous versions of Exchange is the biggest stumbling block toward getting Exchange 2010 deployed. There are two other minor compatibility issues that you need to be aware of though. First, you cannot perform an in-place upgrade from Exchange 2007 to Exchange 2010. Of course, that probably isn't a big surprise, considering the other compatibility issues. Second, Exchange 2010 will install only on Windows Server 2008 with SP2 or higher installed.

The big questions

Given these various compatibility issues, there are a couple of big questions that really need to be answered. First, why did Microsoft choose to make a version of Exchange that isn't really backward-compatible with previous versions? Second, is there going to be a big backlash against Exchange 2010?

I won't pretend to know all the reasons why Microsoft has designed Exchange 2010 the way that they did. What I have heard, though, is that Microsoft built Exchange 2010 from the ground up so that it would be more scalable than previous versions. Remember that Exchange 2010 is the first version of Exchange to also be offered as a service, and Microsoft therefore needed to design Exchange in a way that would allow it to scale to millions of mailboxes.

As far as whether or not there will be a backlash against Exchange 2010, I think that it is too early to tell. A quick look around Microsoft's message boards reveals a lot of people who are upset about the complexity of Exchange 2010 and its inability to coexist with previous versions of Exchange. Remember that some of those coexistence issues are going to go away when Exchange Server 2007 SP2 is eventually released. For now, all we can do is wait and see what the reaction to Exchange 2010 is once it has been released.


Brien Posey is a seven-time Microsoft MVP. He has written thousands of articles and written or contributed to dozens of books on a variety of IT subjects.

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