Decommission on-premise exchange 2016 servers

Hi @Phillip Guthrie

Thank you for posting your question in the Q&A Forum.

Since you are decommissioning a 4-node DAG and a Witness server in a hybrid environment, Microsoft recommends following the supported operational sequence documented in their decommissioning guidance to ensure your Active Directory remains consistent.

As a moderator, I can provide a high-level roadmap based on that official workflow. The specific commands and implementation details should always be validated directly against the Microsoft documentation for your environment.

Preparation and DNS Transition

The process typically begins with ensuring all DNS records, such as MX, Autodiscover, and SPF, are fully pointed to Microsoft 365. It is also recommended to nullify the Service Connection Point (SCP) on the on-premises servers to prevent internal clients from attempting to connect to the legacy infrastructure.

Hybrid Configuration Removal

The Hybrid Configuration Wizard (HCW) should be used to remove the hybrid configuration. This ensures that organization relationships and connectors are decommissioned through a supported method.

Database Availability Group (DAG) Dismantling

Before uninstallation, the DAG must be dismantled. This generally involves removing all mailbox database copies, evicting the members from the DAG, and then removing the DAG and Witness server objects.

System Mailbox Management

It is necessary to verify that all arbitration, discovery, and audit log mailboxes are either moved or disabled. The Exchange uninstaller is designed to block progress if it detects any remaining mailboxes on the local databases.

Server Uninstallation

The final step is to perform a formal uninstallation through the Programs and Features interface on each server. This is the supported method to ensure that Exchange attributes are removed from Active Directory. Microsoft advises against simply deleting the virtual machines or server objects.

If your organization continues to use Microsoft Entra Connect for directory synchronization, please review Microsoft's guidance regarding the retention of Exchange Management Tools. Since Active Directory remains the source of authority in synchronized environments, these tools may be required for ongoing attribute management.

For the detailed step-by-step checklist and technical procedures, please refer to the following Microsoft Learn article: How and when to decommission your on-premises Exchange servers in a hybrid deployment | Microsoft L…

If you encounter specific errors or prerequisite failures during this process, please provide the error details so the community can assist with further review.

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