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If you are making the move from Exchange 5.5 to Exchange 2003, there are a couple of ways to do it. You can perform an in-place upgrade; or you can bring an Exchange 2003 server into your organization, and then migrate resources from the Exchange 5.5 server to the Exchange 2003 server.
The case for migration vs. in-place upgrade
In many cases, a migration is more practical than an upgrade. After all, if a server is still running Exchange 5.5, it's probably on old hardware too that may not be up to the job of running Exchange Server 2003.
Migrating also gives you the chance to move mailboxes gradually and avoid any extended user downtime. For example, you could move two or three mailboxes, make sure there are no problems, move a few more, and so on.
Preventing Exchange mailbox corruption
The actual process of moving mailboxes from one server to another is simple, but things can potentially go wrong. Mailbox corruption could rear its ugly head, resulting in data loss. Fortunately, there are a few tricks you can use to help prevent this from happening.
(I am assuming you already have a new Exchange 2003 server up and running, and that the Exchange 2003 server and the Exchange 5.5 server can see each other.)
The first thing I recommend is taking a moment to verify that the account you will be logged in with has sufficient permissions. The account must have Exchange admin permissions for both Exchange servers. It must also be a member of the Domain Admins group. This is important, because the account must be able to change some of the account properties linked to the mailboxes you're migrating.
After you've verified your account permissions, do a little clean-up work. For example, ask users to empty their Deleted Items folder and any Junk Mail folders. Doing so will greatly reduce the mailbox size in many cases, and help to expedite the move.
The Exchange Administrator program that comes with Exchange 5.5 also has a Clean Mailbox option you can use to do some cleanup work. (Whether you want to use this tool or not depends on your e-mail retention policies for old messages.) The basic idea behind the tool is that it allows you to erase messages older than a certain date or larger than a specific size. To use the Clean Mailbox tool, simply select the target mailbox and then choose Tools -> Clean Mailbox.
Fixing Exchange Server inconsistencies
Inconsistencies between the Exchange 5.5 directory and Windows Active Directory can also cause problems during a mailbox migration. An example is when there is a reference to a mailbox in the Exchange 5.5 directory, but the information store doesn't contain a mailbox by that name.
Another inconsistency is an invalid access control list entry. This tends to happen in Exchange 5.5 environments when someone is given permissions to a mailbox other than their own, but then leaves the company. The account is deleted, but access control entries pointing to it might still exist in mailboxes the former employee had rights to.
There is a tool that will resolve inconsistencies prior to the migration called PrivFoldCheck. It is a part of the Exchange Server Exchange Deployment Tools. You can download the tools here.
The PrivFoldCheck tool reviews all access control list entries on each mailbox. If it finds an access control entry for an account that no longer exists, it deletes it. The tool also runs a directory service-information store consistency check to resolve any issues between the two.
Fixing corrupted Exchange mailboxes
The last issue you need to address prior to an Exchange 5.5 to Exchange 2003 migration is corrupted mailboxes. Microsoft Exchange considers a mailbox to be corrupt if the mailboxes' various attributes are in an inconsistent state, or if key attributes are missing.
Exchange can become confused when Exchange 2003 is brought into an Exchange 5.5 environment. For example, if an account has an Exchange 5.5 mailbox, the mailbox-enabled attribute is applied. If an account is linked to an Exchange 2003 mailbox, the mail-enabled attribute is also applied. So, sometimes, both attributes get applied. Exchange subsequently becomes confused and thinks the mailbox is corrupt.
To prevent attribute-related inconsistencies from ruining your migration, I recommend running the RecipientDSInteg tool on your Exchange 5.5 mailboxes first. If inconsistencies are found, you can use the LDIFDE utility to correct them. RecipientDSInteg is also part of the Exchange Server Exchange Deployment Tools. LDIFDE is built into Windows.
About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. Brien has served as CIO for a nationwide chain of hospitals and was once in charge of IT security for Fort Knox. As a freelance technical writer he has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at http://www.brienposey.com.
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Related information from SearchExchange.com:
Learning Guide: Exchange migration
Tip: Drawbacks of running a mixed mode Exchange Server environment
Ask the Expert: Common mistakes when upgrading to Exchange 2003
Reference Center: Exchange mailbox management
