As Exchange Server 2016 approaches its end of extended support on October 14, 2025, organizations using Exchange Server 2019 will need to plan for decommissioning their 2016 environments. This guide outlines the key steps and considerations for removing Exchange 2016 from an environment that already has Exchange 2019 installed.

Why Decommission Now?

If you plan to stay on-premises, moving to Exchange 2019 as soon as possible is highly recommended. Exchange 2019 will support in-place upgrades to Exchange Server Subscription Edition (SE), making it the first version in years to allow such upgrades. By decommissioning Exchange 2016 servers now, you’ll be prepared for a smoother transition to Exchange SE when it becomes available.

Preparation Steps

Inventory and Upgrade Third-Party Applications

Before beginning the decommissioning process:

  1. List all applications using Exchange 2016 servers
  2. Configure these applications to use the newer Exchange Server infrastructure
  3. Verify with application providers that they support your latest Exchange version

Review Client Access Services

Ensure all client connectivity namespaces are routing to the latest Exchange servers. This includes:

  • Reviewing Exchange virtual directory namespaces
  • Verifying client connections (ActiveSync, Outlook, EWS, OWA, OAB, POP3/IMAP, Autodiscover)
  • Reviewing Service Connection Point objects in Active Directory

Mailflow Considerations

Audit your mail flow configuration:

  • Review and update send connectors
  • Recreate receive connectors on new Exchange servers
  • Check SMTP logs for any services still sending traffic to old servers

Mailbox Migration

All Exchange 2016 mailboxes must be moved to the newer Exchange version before decommissioning. Key steps include:

  1. Migrating all mailbox types (user, arbitration, public folder)
  2. Removing completed move requests and migration batches
  3. Verifying no mailboxes remain on Exchange 2016 servers

Decommissioning the Database Availability Group (DAG)

  1. Remove all mailbox database copies
  2. Remove mailbox databases
  3. Remove DAG members
  4. Delete the DAG itself

Final Steps

  1. Put Exchange 2016 servers into maintenance mode for a week to observe any issues
  2. Remove Exchange 2016 health mailboxes
  3. Uninstall Exchange 2016 following best practices
  4. Perform post-uninstallation tasks like cleaning up DNS records and removing server objects

.A comprehensive guide, Decommissioning Exchange Server 2016, can be found on the Exchange Team Blog.