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Avoid these Exchange Server migration pitfalls

Plenty of IT shops are still moving from legacy versions of Exchange to 64-bit Exchange Server 2007. When should they look into migrating to Exchange 2010?

Microsoft will release Exchange Server 2010 later this year, but there are still plenty of enterprises on Exchange 2000 and 2003 that are now migrating to Exchange 2007.

Mike Crowley

Mike Crowley, an enterprise and messaging administrator with Planet Technologies, Inc., a Germantown, Md.-based integrator, has some advice for those moving to 64-bit Exchange Server 2007.

What is the most common problem IT administrators run into when upgrading from Exchange Server 2003 to Exchange Server 2007?

Mike Crowley: The number one gotcha is the fact you cannot "upgrade" Exchange 2003. You must migrate services and mailbox content to another server. This is primarily because of the change in CPU requirements. Exchange 2003 can only be on x86 systems and Exchange 2007 can only be x64 systems, as well as Exchange Server 2010. For small businesses that plan to reuse the same hardware (assuming it's x64 capable), this means they have to move everything out and then move it all back. For large businesses, this means significant hardware purchases.

Microsoft has not yet divulged much information on migration to Exchange Server 2010, but it looks like customers on Exchange 2003 might want to wait until the end of the year, rather than migrating twice.

How much downtime should administrators plan for to complete migration of 100 mailboxes from Exchange 2000 or Exchange 2003 to an x64 version?

Crowley: Fortunately, the downtime is very minimal for Exchange 2007 migrations. This is because the downtime is really only for the duration of an individual's mailbox move. In fact, while I don't recommend it, if users are in Outlook cached mode they can keep typing emails while they are being moved. When their mailboxes are done being moved, all they have to do is restart Outlook.

Realistically, I'd say a 100-user mailbox move can easily be done over a weekend. I like to set the expectation of an outage even if it isn't necessary, just so we have wiggle room. The overall migration takes longer than this, but the pieces can be built without incurring downtime.

While there are good references out there, the migration process is not for the Exchange newcomer. Introducing an Exchange 2007 server in the environment has drastic implications on mail flow behavior for organizations with multiple locations. In my experiences, the Exchange upgrade is also often tied to an Active Directory upgrade.

How can an Exchange migration affect mail flow?

Crowley: The basic idea is Exchange 2003 and earlier versions use Routing Groups to determine how mail flows from branch office to branch office, etc. With Exchange 2007, all servers are placed in one Routing Group, regardless of where they physically sit. This means we [administrators] have to trick Exchange 2000/2003 to deliver mail to the right location. Otherwise, mail for a user in Maryland from another user in Maryland might be routed through the Okinawa branch office.

More on Exchange migrations:
Exchange Server 2007 support ends at Windows Server 2008

Microsoft Exchange Server study guide

New features in Microsoft Exchange Server 2010

Are there any other significant differences between Exchange Server 2003 and newer versions that could cause problems during a migration?

Crowley: Exchange 2007 handles many back-end processes differently than Exchange 2000 and Exchange 2003. You have to run some scripts to update address lists, which can be tricky if you have many custom address lists, as well as use the feared Active Directory Services Interface edit tool for removing some old Exchange services.

[Another consideration] is SSL Certificate use in Exchange 2007; it can differ from Exchange 2003 because Exchange 2007 supports certificates with multiple names. The certificates require some PowerShell commands to generate them, and frequently confuse people while configuring and purchasing.

Small and medium-sized businesses often have a misconception about the new Exchange Server roles. If you read TechNet, you might get the impression that you need multiple Exchange 2007 servers to do what one Exchange 2003 server does. This is not true. These server roles allow you to break Exchange into many pieces if necessary, but Exchange 2007 can do everything Exchange 2003 can by running it on a single server.

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