The reasons are as varied as the components within Exchange itself:
Enable transport services: Set-ServerComponentState -Identity -Component HubTransport -State Active -Requester Maintenance
Once your updates are finished and the server has rebooted, you must reverse the process to bring it back into production:
The server stops accepting new connections and requests from three key sources:
This step ensures that all active mailbox databases are moved to other healthy nodes in the DAG.
Before you begin your updates, verify the state of the server with this command: Get-ServerComponentState -Identity
When an Exchange Server is placed in maintenance mode, administrators want to ensure that end-users are notified and emails are redirected to a alternate server or a designated mailbox to minimize downtime and prevent email loss. The "Maintenance Mode Notification and Redirect" feature provides a seamless way to notify users and redirect emails during maintenance.
The "ServerWideOffline" component should show as "Inactive." Taking the Server Out of Maintenance Mode
When an Exchange server is placed into maintenance mode—typically via the Exchange Admin Center (EAC) or the Set-ServerComponentState PowerShell cmdlet—it is not simply being “turned off.” Rather, it is being gracefully told to step out of the active rotation. Think of it as a relief pitcher warming up in the bullpen while the starter is pulled from the game.
Finally, put the server into a full maintenance state. This notifies the Exchange ecosystem that the server is officially offline for servicing.