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Error: Re-install Exchange 2016 CU22 on new Windows Server 2016 with same IP and name

Paul Siso 256 Reputation points
2025-08-25T19:56:33.47+00:00

We have a development environment, one Exchange 2016 CU22 mail server and one Exchange Edge 2016 CU23. A previous admin tried to install Exchange mail server, but could not get it to run, so now I'm trying to reinstall Exchange on a brand new Windows Server 2016, with the same Exchange 2016 CU22 on it, to see if it can fully restore itself. I'm getting the errors below. We attempted to delete the database from ADSI edit, but got the second error below. What's the best route on how to proceed, should I delete the Exchange mail server name from ADSI edit and attempt the install again?

Error 1:
        " was run: "Microsoft.Exchange.Configuration.Tasks.ManagementObjectNotFoundException: Couldn't find database "Mailbox Database 1701523402". Make sure you have typed it correctly.

   at Microsoft.Exchange.Configuration.Tasks.DataAccessTask1.GetDataObject[TObject](IIdentityParameter id, IConfigDataProvider session, ObjectId rootID, OptionalIdentityData optionalData, Func2 notFoundError, Func`2 multipleFoundError, ExchangeErrorCategory errorCategory)

   at Microsoft.Exchange.Management.RecipientTasks.GetMailboxOrSyncMailbox`1.<>c__DisplayClass68_0.<SetDefaultRetentionValues>b__0()

   at Microsoft.Exchange.Data.Directory.ProvisioningCache.ProvisioningCache.TryAddAndGetGlobalDictionaryValueT,K

   at Microsoft.Exchange.Management.RecipientTasks.GetMailboxOrSyncMailbox`1.SetDefaultRetentionValues(Mailbox mailbox)

   at Microsoft.Exchange.Management.RecipientTasks.GetMailboxOrSyncMailbox`1.ConvertDataObjectToPresentationObject(IConfigurable dataObject)

   at Microsoft.Exchange.Management.RecipientTasks.GetMailbox.ConvertDataObjectToPresentationObject(IConfigurable dataObject)

   at Microsoft.Exchange.Configuration.Tasks.GetRecipientObjectTask`2.WriteResult(IConfigurable dataObject)

   at Microsoft.Exchange.Configuration.Tasks.GetTaskBase1.WriteResult[T](IEnumerable1 dataObjects)

   at Microsoft.Exchange.Configuration.Tasks.GetTaskBase`1.InternalProcessRecord()

   at Microsoft.Exchange.Configuration.Tasks.GetObjectWithIdentityTaskBase`2.InternalProcessRecord()

   at Microsoft.Exchange.Configuration.Tasks.GetRecipientObjectTask`2.InternalProcessRecord()

   at Microsoft.Exchange.Management.RecipientTasks.GetRecipientWithAddressListBase`2.InternalProcessRecord()

   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__91_1()

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

Error 2 (after deleting the database):

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

   at Microsoft.Exchange.Configuration.Tasks.Task.ThrowError(Exception exception, ErrorCategory errorCategory, Object target, String helpUrl)

   at Microsoft.Exchange.Configuration.Tasks.Task.WriteError(Exception exception, ErrorCategory category, Object target, Boolean reThrow)

   at Microsoft.Exchange.Configuration.Tasks.DataAccessTask`1.Validate(TDataObject dataObject)

   at Microsoft.Exchange.Configuration.Tasks.SetTaskBase`1.InternalValidate()

   at Microsoft.Exchange.Configuration.Tasks.SetRecipientObjectTask`3.InternalValidate()

   at Microsoft.Exchange.Management.Common.SetMailEnabledRecipientObjectTask`3.InternalValidate()

   at Microsoft.Exchange.Management.RecipientTasks.SetUserBase`3.InternalValidate()

   at Microsoft.Exchange.Management.RecipientTasks.SetMailboxBase`3.InternalValidate()

   at Microsoft.Exchange.Management.RecipientTasks.SetMailbox.InternalValidate()

   at Microsoft.Exchange.Configuration.Tasks.Task.<ProcessRecord>b__91_1()

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

Exchange | Exchange Server | Other
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Accepted answer
  1. Vergil-V 3,675 Reputation points Microsoft External Staff Moderator
    2025-08-26T06:54:31.8+00:00

    Hi @Paul Siso 
    Thanks for reaching out to the Microsoft Q&A forum.    
    Based on your description, I understand that you're attempting to re-install Exchange Server 2016, but the process is incomplete due to two errors: Error 1: Couldn't find database and error 2: Database is mandatory on UserMailbox 

    As a forum moderator, I don’t have access to a dedicated testing environment to replicate user-specific scenarios. That said, my response is primarily based on official Microsoft documentation, and I’m happy to share what I’ve found that may help provide more context and guidance. 

    From my research, if the error 'Database is mandatory on UserMailbox' appears (Error 2), it is highly likely to persist even if you attempt to resolve 'Couldn't find database' (Error 1) by using Remove-MailboxDatabase to delete the database. 

    This is because the underlying issue often involves user mailboxes that still reference a missing or null homeMDB attribute. To resolve this, you can use the following PowerShell command to identify accounts with an empty homeMDB attribute: 

    Get-ADUser -Filter -Properties | where{$.legacyExchangeDN -ne $null -AND $.homeMDB -eq $null} | ft Name  

    Once identified, you can update the homeMDB attribute to a valid value (i.e., not null). After that, you should be able to delete the account, which helps resolve the issue. 

    For more context, you can refer to this article where another member encountered the same issue: [exchange 2016] Database is mandatory on usermailbox. - Microsoft Q&A 

    I sincerely hope this information partially clarifies your situation and assists you in planning your solution. Please do not hesitate to reply if you have any updates.  

    Thank you for your understanding.  

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.   

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  1. Paul Siso 256 Reputation points
    2025-08-26T20:10:58.5466667+00:00

    That worked! Thank you.

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