Troubleshoot Exchange 2016 Error Database is mandatory on UserMailbox

Recently I have been working with a customer to upgrade from Exchange Server 2010 to Exchange Server 2016 and run into an issue. During the installation, Exchange setup failed on step 9 with below error message.

Troubleshoot Exchange 2016 Error Database is mandatory on UserMailbox

Looking at the error message in detail i noticed the following error.

The following error was generated when “$error.Clear();

if ( ($server -eq $null) -and ($RoleIsDatacenter -ne $true) )


Update-RmsSharedIdentity -ServerName $RoleNetBIOSName


” was run: “Microsoft.Exchange.Data.DataValidationException: Database is mandatory on UserMailbox.

at Microsoft.Exchange.Data.Directory.ADDataSession.Save(ADObject instanceToSave, IEnumerable`1 properties, Boolean bypassValidation)

at Microsoft.Exchange.Data.Directory.Recipient.ADRecipientObjectSession.Save(ADRecipient instanceToSave)

at Microsoft.Exchange.Management.Deployment.UpdateRmsSharedIdentity.Link()

at Microsoft.Exchange.Management.Deployment.UpdateRmsSharedIdentity.InternalProcessRecord()

at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__b()

at Microsoft.Exchange.Configuration.Tasks.Task.InvokeRetryableFunc(String funcName, Action func, Boolean terminatePipelineIfFailed)”.

How to Fix It?

As you can see from the error message that Exchange Server 2016 installation is trying to retrieve a system mailbox with the name of “SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c}“. This error message is being caused by system mailbox that does not have mailbox database associated with the mailbox. I have seen this scenario where you have not decommissioned your Exchange server properly. To verify this issue, run the following Exchange Management Shell (EMS) cmdlet.

Get-Mailbox -Arbitration | ft Name, ServerName, Database -Auto

Troubleshoot Exchange 2016 Error Database is mandatory on UserMailboxAs you can see, I had two mailboxes that do not have mailbox database assigned. In active directory theses accounts exist in default Users OU.To fix this issue,, delete these accounts from active directory and wait for AD replication. Once the AD replication is completed, re-run the cmdlet to verify the system mailboxes have been deleted from Exchange Server.

Troubleshoot Exchange 2016 Error Database is mandatory on UserMailboxFor more information on Exchange 2016, please go through the following blog posts.