Exchange Server 5.5, once a robust solution, is quickly approaching the end of its life(cycle). Microsoft no longer provides support or security updates for this version, making it vulnerable to potential security breaches and compatibility issues with modern email clients. Upgrading to Exchange 2000 offers several benefits:

1. Improved Security: Exchange 2000 includes security enhancements that protect your email infrastructure from emerging threats.

2. Enhanced Collaboration: Features like improved calendaring and integration with Outlook 2000 provide enhanced collaboration capabilities.

3. Better Scalability: Exchange 2000 offers improved scalability, allowing you to support a growing user base and increasing email demands.

4. Streamlined Administration: The introduction of Active Directory integration simplifies user management and administrative tasks.

Planning the Migration:

Ensure Exchange 5.5 Service Pack 4 has been installed:
Of course patch the previous exchange installation before upgrading.

Forest Preparation:
Before installing Exchange 2000, you need to prepare the Active Directory forest to accommodate the new Exchange version. This involves extending the schema.
To perform forest preparation, open a command prompt and navigate to the Exchange 2000 installation medium (X drive in my case):

Domain Preparation:
After forest preparation is complete, you should perform domain preparation. This step prepares the individual domains within your Active Directory for Exchange 2000 installation.
Run the following command to prepare the domain:

Install Exchange 2000:
Begin by installing Exchange 2000 on new servers. This allows for a parallel coexistence with your existing Exchange 5.5 environment.
Installation Command:

Connector Configuration:
Set up connectors between Exchange 5.5 and Exchange 2000 to enable communication between the two systems. This can be done in the ESM console.
Either use machine-name, or private ip-addresses; and ensure HTTP/S and SMTP port numbers are open on any firewall in-between.

Migrate Mailboxes:
Migrate user mailboxes gradually from Exchange 5.5 to Exchange 2000 using tools like the Active Directory Connector (ADC) and Exchange Migration Wizard.
Migration Command (Active Directory Connector):

Public Folder Migration:
If you use public folders ( i know we do), plan and execute their migration to the Exchange 2000 instance.
Migration Command (Public Folder Replication):

Client Updates:
Update email clients to versions compatible with Exchange 2000, such as Outlook 2000 or later.
Ensure that clients are configured to connect to the new Exchange 2000 servers (use the outlook system tray icon, right click > view status)

Testing:
Rigorously test the new Exchange 2000 environment to ensure that email flows smoothly, and users experience minimal disruptions.
Use the following commands to verify database and service status:

Database Integrity Check:

Check Service Status:

Once you have successfully migrated your users and data to Exchange 2000 and ensured the new environment's stability, it's time to decommission the legacy Exchange 5.5 instance. This process involves removing Exchange 5.5 from your organization, but it should be approached with caution to prevent any data loss or disruptions. Here are the steps for decommissioning:

Verify Data Migration: Before proceeding, double-check that all user mailboxes, public folders, and other essential data have been successfully migrated to Exchange 2000. Ensure that users are comfortably using the new environment.

Backup Exchange 5.5: Take a final backup of your Exchange 5.5 servers, including the mailbox and public folder databases. This is a precautionary step to ensure you have a backup of your data in case anything unexpected happens during decommissioning.

Confirm Routing and Connector Migration: Ensure that all mail routing and connectors have been switched to Exchange 2000. Confirm that mail is flowing correctly through the new environment. TIP: Shutdown the exchange 5.5 instance for a week or so, and capture any/all errors/warnings from event logs, and dismiss anything relating to internal replication.

Disconnect Exchange 5.5: After bringing the Exchange 5.5 servers back online; disconnect the Exchange 5.5 servers from the exchange organisation, by disabling the SMTP connectors and SMTP services on the Exchange 5.5 servers using Exchange System Manager > Connectors > Right Click > Properties > General Tab, remove Local Bridgehead Servers, with exchange 5.5 installed. Ensure there are bridgehead servers avaialble for SMTP communication still.
TIP: To ensure Exchange 'reads' this config change, restart all `Microsoft Exchange Routing Engine` services

Monitor for Inbound Mail: Keep an eye on the Exchange 5.5 servers for a period to confirm that they are no longer receiving incoming emails. Ensure that all mail is now being routed through Exchange 2000. You can do this from the IIS Snapin.

Public Folder Replication: If you were using public folders in Exchange 5.5, ensure that public folder replication has been completed to Exchange 2000. Confirm that all public folder data is accessible and up to date in the new environment. You may find that outlook on all your clients required a software update, in order to access the Exchange 2000 public folders.

User Access Validation: Verify that users can access their own mailboxes and public folders in Exchange 2000 without any issues. Conduct basic user testing to confirm that everything is functioning as expected. It's probably a good idea to sit back for a couple of days, to make sure, any and all issues are captured by the support-desk.

Gradual Server Decommissioning: Once you are confident that Exchange 5.5 is no longer in use, you can proceed with the decommissioning process. This typically involves shutting down and removing the Exchange 5.5 servers from the network.

Sorry i forgot to capture the output of the above remove command.Final Backup: Take a final backup of any critical data on the Exchange 5.5 servers that you may need for reference or auditing purposes.

Documentation: Document the decommissioning process, including the date of decommissioning, any issues encountered, and the final configurations. You know "Change Control"..

Security and Permissions: Review and revoke any unnecessary permissions or administrative rights associated with the legacy Exchange 5.5 servers. Can be achieved via ADSI edit; and ESM in tandem.

DNS Records: Update your DNS settings and MX (Mail Exchange) records to ensure they no longer point to the decommissioned Exchange 5.5 servers. This prevents any accidental mail delivery to the old environment.

One last log-file check: Pro-actively go and look to see if your exchange server's logs

Monitoring:
Continuously monitor the new Exchange 2000 environment for any issues, especially during the post-migration period.
Use Exchange System Manager and Event Viewer for monitoring.

Training:
Provide technical staff with training, and offer guidence and support to users, ensuring everyone benefits from the new features Exchange 2000 offers.

Documentation:
Maintain detailed documentation of the migration process, configurations, and any issues encountered for future reference.