Exchange 2016: “Database is mandatory on UserMailbox”

When you are setting up a new exchange server to upgrade the current exchange server, with all the prerequisite has been applied and the next step is the run the setup.exe file of the exchange CU. However, you notice that the interface of the setup has stop at Step 7 which is “Mailbox role setup” because of an error encounter.

Usually the interface doesn’t really provide you the detail reason of error occur.

“Mailbox role: Transport service : Error”


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To know get more understanding of the error, Go to > Windows Explorer > open C:\ Drive > Select Exchange Setup Log Folder > Open Exchange Setup txt file > Scroll to the bottom to get the details.



*Error: Database is mandatory on UserMailbox;

Below is the sample logs and error that causes the setup to stop, and it seems that there is a system mailbox “SystemAttendantDependent_xxx” found corrupted. Usually if is corrupted means that this account’s the value of HomeMDB attribute is empty. The solution to this is to add the correct value for HomeMDB attribute of the corrupted account.


Here how it is done;

  1. To find whether are there any other corrupted mailboxes;
    • Open your current exchange server’s powershell
    • Run this command
      • Get-Mailbox -Arbitration | Select Name, Database
      • Then it will show you number of corrupted mailboxes with WARNING stated
  2. Go to ADSI Edit > Connect to Default naming context  > Users container > search for a valid user account with mailbox > Open properties
  3. Find the attribute HomeMDB > Copy the value (*Optional: You can paste the value into a notepad for temporary)
  4. Go to ADSI Edit > Connect to Default naming context  > Users container > search for a corrupted account > Open properties
  5. Find the attribute HomeMDB > Replace the empty box with the copied value
  6. * Do this for corrupted mailboxes that you found, which is blocking your success to complete setup of your new exchange.
  7. Rerun the setup.exe
  8. If successful setup than continue with the post-installation.


There could be other related corrupted account (Can’t be find from the exchange powershell) that has blocking your success to complete setup of your exchange. Please look into details of the logs to find out what are the other corrupted accounts and replace their empty value attribute with the correct ones.

Author: sabrinaksy

Just an ordinary lady who love what she does best.

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