Uninstalling an old Exchange server: mailboxes, connectors and errors that block removal

Once the mailboxes have moved to your new servers, removing the old Exchange server should be a formality, until setup's readiness checks stop with a long message about mailboxes you can't see. Here's what blocks the uninstall, the hidden mailbox types behind the error, the DAG and connector clean-up to do first, and how to confirm the server has gone cleanly.

Symptoms#

Uninstall (from Control Panel › Programs and Features or Setup.exe /Mode:Uninstall) fails its readiness checks with an error like this. You get the same text if you run Remove-MailboxDatabase yourself:

This mailbox database contains one or more mailboxes, mailbox plans, archive mailboxes,
public folder mailboxes or arbitration mailboxes, Audit mailboxes. To get a list of all
mailboxes in this database, run the command Get-Mailbox -Database <Database ID>. ...
To get a list of all Audit mailboxes in this database, run the command
Get-Mailbox -Database <Database ID> -AuditLog. ...

Related problems on the same job:

• A Windows Installer prompt: The feature you are trying to use is on a CD-ROM or other removable disk that is not available. followed by Insert the 'Microsoft Exchange Server' disk and click OK.
• Setup refuses to continue because the server is still a member of a database availability group (DAG).
• No error, but afterwards outbound mail queues because a Send connector lost its only source server, or a scanner relaying through the old server stops sending.

Why it happens#

Uninstall has to remove the server's mailbox databases, and Exchange won't delete a database that still hosts user, archive, public folder, arbitration or audit mailboxes. The catch is that plain Get-Mailbox -Database only returns ordinary mailboxes. System mailboxes hide behind switches:

The Windows Installer prompt has a different cause: the installer needs the original media for the CU that's currently installed and can't find it.

How to fix it#

1. Inventory every mailbox on the old server#

In a multi-domain forest, widen the shell's scope first or you'll miss mailboxes in other domains. Then check each database on the server:

Set-ADServerSettings -ViewEntireForest $true
Get-MailboxDatabase -Server EX2016-01 | Format-Table Name, Server

$db = 'DB2016-01'
Get-Mailbox -Database $db -ResultSize Unlimited | Format-Table Name, RecipientTypeDetails
Get-Mailbox -Database $db -Arbitration | Format-Table Name, Database
Get-Mailbox -Database $db -AuditLog | Format-Table Name, Database
Get-Mailbox -Database $db -PublicFolder | Format-Table Name, Database
Get-Mailbox -ResultSize Unlimited | Where-Object { $_.ArchiveDatabase -eq $db } |
  Format-Table Name, Database, ArchiveDatabase

2. Move what has to move#

$target = 'DBSE-01'
$batch  = 'Decom-EX2016-01'
Get-Mailbox -Database $db -ResultSize Unlimited | New-MoveRequest -TargetDatabase $target -BatchName $batch
Get-Mailbox -Database $db -Arbitration  | New-MoveRequest -TargetDatabase $target -BatchName $batch
Get-Mailbox -Database $db -AuditLog     | New-MoveRequest -TargetDatabase $target -BatchName $batch
Get-Mailbox -Database $db -PublicFolder | New-MoveRequest -TargetDatabase $target -BatchName $batch
Get-Mailbox -ResultSize Unlimited | Where-Object { $_.ArchiveDatabase -eq $db -and $_.Database -ne $db } |
  New-MoveRequest -ArchiveOnly -ArchiveTargetDatabase $target -BatchName $batch

Get-MoveRequest -BatchName $batch | Get-MoveRequestStatistics |
  Format-Table DisplayName, StatusDetail, PercentComplete -AutoSize

When everything shows Completed, clear the requests with Get-MoveRequest -BatchName $batch | Remove-MoveRequest. Then remove the databases yourself with Remove-MailboxDatabase: if anything is left, you get the same error much faster than through setup. The cmdlet doesn't delete the .edb and log files; delete those later.

3. Take the server out of the DAG#

Get-MailboxDatabaseCopyStatus -Server EX2016-01 | Format-Table Name, Status
Move-ActiveMailboxDatabase -Server EX2016-01            # if it still holds active copies
Remove-MailboxDatabaseCopy -Identity 'DB2016-02\EX2016-01' -Confirm:$false
Remove-DatabaseAvailabilityGroupServer -Identity DAG2016 -MailboxServer EX2016-01

If the server is already dead, Remove-DatabaseAvailabilityGroupServer has a -ConfigurationOnly switch; you then evict the node from the Windows failover cluster as well. When you remove the last member, delete the DAG with Remove-DatabaseAvailabilityGroup.

4. Re-point connectors and anything that sends SMTP to the server#

Get-SendConnector | Format-Table Name, SourceTransportServers -AutoSize
Set-SendConnector -Identity 'Internet' -SourceTransportServers EXSE-01, EXSE-02
Get-ReceiveConnector -Server EX2016-01 | Format-Table Name, Bindings, RemoteIPRanges -AutoSize

• Custom Receive connectors (relay, partner TLS) belong to the server and disappear with it. Recreate them on the new servers, then use the SMTP receive protocol logs under %ExchangeInstallPath%TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive (with protocol logging enabled on the connector) to find devices still connecting to the old server.
• In hybrid, re-run the Hybrid Configuration Wizard and choose the new servers for transport rather than editing the hybrid connectors by hand (see Exchange hybrid mail flow).
• Take the server out of load balancer pools, DNS records, firewall rules, backup jobs and monitoring.

5. Run the uninstall#

Mount the ISO of the CU that's installed on the old server (Get-ExchangeServer EX2016-01 | Format-List AdminDisplayVersion tells you which). That avoids the "Insert the 'Microsoft Exchange Server' disk" prompt; if it still appears, browse to the mounted media. Then, from an elevated prompt:

D:\Setup.exe /Mode:Uninstall /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF

If it fails, read the end of C:\ExchangeSetupLogs\ExchangeSetup.log or run SetupLogReviewer.ps1 from Microsoft's CSS-Exchange scripts against it.

6. Clean up afterwards#

• Health mailboxes whose database no longer exists can be deleted from Microsoft Exchange System Objects › Monitoring Mailboxes in Active Directory Users and Computers (turn on View › Advanced Features if you can't see it). Left behind, they tend to surface as MSExchange ADAccess warnings (Event ID 2937) about attributes pointing to deleted objects.
• If a server died and can't be uninstalled, the supported route is to rebuild it with the same name, run Setup.exe /Mode:RecoverServer and then uninstall properly. Deleting objects with ADSI Edit is a last resort.

Verify the fix#

Get-ExchangeServer | Format-Table Name, AdminDisplayVersion -AutoSize
Get-MailboxDatabase | Format-Table Name, Server -AutoSize
Get-DatabaseAvailabilityGroup | Format-Table Name, Servers -AutoSize
Get-SendConnector | Format-Table Name, SourceTransportServers -AutoSize
Get-Mailbox -Arbitration | Format-Table Name, ServerName, Database -AutoSize

Good looks like this: the old server appears nowhere in that output, the arbitration mailboxes sit on the new servers, test messages flow both ways, Get-Queue is clean and Outlook still connects.

Key takeaways#

• Arbitration, audit and public folder mailboxes, and archives stored apart from their primary mailbox, don't appear in a plain Get-Mailbox -Database.
• Empty and remove the databases yourself before running setup.
• Fix Send connectors, relay devices and hybrid settings before the server disappears.
• Keep the ISO of every CU you install; uninstall needs it.
• Migrating from Exchange 2016? This is the last step of moving from Exchange 2016 to Exchange Server SE.

References#

• Error when you try to remove a mailbox database (Microsoft Learn)
• Manage database availability groups in Exchange Server (Microsoft Learn)
• Fix failed Exchange Server updates (Microsoft Learn)