Arbitration mailboxes are system mailboxes used by Exchange Server system to store different types of system data and to manage message approval workflows. The main purpose of these mailboxes is to moderate emails. There are five arbitration mailboxes in Exchange Server 2016. However, from Exchange Server 2016 onwards, there are seven mailboxes.
Why do you need to remove and recreate the arbitration mailboxes?
The system mailboxes can get damaged due to human errors or various other issues. Some common issues include:
- Hardware failure.
- Backup software or antimalware software is not compatible with the Exchange Server version.
- Updates to the system didn’t complete successfully or stopped abruptly.
- Malware or ransomware infection.
- Sudden interruption of power, leading to improper shut down of the databases.
Removing the System Mailboxes
Before proceeding to remove the system mailboxes, you need to get the exact version of your Exchange Server installation as you would need it while recreating the system mailboxes. To get the version and build number of Exchange Server, run the following command.
Get-ExchangeServer | Select-Object AdminDisplayVersion
As mentioned, there are seven system mailboxes, which include five system mailboxes, one federation mailbox, and one migration mailbox. To confirm this, run the Get-Mailbox PowerShell command as given below.
Get-Mailbox -Arbitration | ft name, alias, servername
The same mailboxes will have their counterpart user in the Active Directory Users and Groups, under the Users Organization Unit (OU).
There is one system mailbox, which acts as the audit mailbox. To confirm which one is the audit mailbox, you can use the following command:
Get-Mailbox -AuditLog | ft name, alias, servername
After taking a note of all the system mailboxes, you can proceed to delete the actual users from the Active Directory Users and Groups. Make sure that only the arbitration mailboxes will be selected and deleted.
To delete the mailboxes, highlight the said mailboxes using the Get-Mailbox command, right-click, and click on Delete.
Next, delete the assigned audit log mailbox.
If you re-run the command to view the mailboxes, you will notice that the result will be empty.
Recreating the Mailboxes
You need to either download the Exchange Server ISO image or locate the server image from your repository. In case you need to download, you can find the exact build ISO file here.
Once downloaded, mount the ISO file by right-clicking on it and then clicking on Mount (How to Mount/Dismount Mailbox Databases).
Once the mount is complete, open Command Prompt as administrator and run the following command.
Setup.exe /IAcceptExchangeServerLicenseTerms_DiagnosticDataOFF /PrepareAD
After this, open the Active Directory Users and Computers to verify that eight mailboxes have been created. Run the following commands to confirm that the mailboxes against the new users have been created successfully.
Get-Mailbox -Arbitration | ft name, alias, servername
Get-Mailbox -AuditLog | ft name, alias, servername
The next step is to enable the mailboxes. For this, run the following commands. The full GUID name can be taken from the commands executed above.
To enable the new Microsoft Exchange Federation Mailbox:
Enable-Mailbox -Identity "<federation guid>" -Arbitration
Set-Mailbox -Identity "<federation guid>" -Arbitration -ProhibitSendQuota 1MB -Force
To enable the new Microsoft Exchange Migration Mailbox:
Enable-Mailbox -Identity "<migration guid>" -Arbitration
Set-Mailbox -Identity "<migration guid>" -Arbitration -Management $true -ProhibitSendQuota 300MB -Force
To enable the Microsoft Exchange Approval Assistant Mailbox:
Get-User -ResultSize Unlimited | where {$_.Name -like "system-mailbox guid"} | Enable-Mailbox -Arbitration
To enable the Microsoft Exchange Organization Mailbox for OAB:
Enable-Mailbox -Identity "<system-mailbox guid>" -Arbitration
Set-Mailbox -Identity "<system-mailbox guid>" -Arbitration -UMGrammar $true -OABGen $true -GMGen $true -ClientExtensions $true -MessageTracking $true -PstProvider $true -MaxSendSize 1GB -Force
Update-OfflineAddressBook -Identity "<offline address book name>"
To enable the Microsoft Exchange Discovery System Mailbox:
Enable-Mailbox -Identity "<system-mailbox guid>" -Arbitration
Set-Mailbox -Identity "<system-mailbox guid>" -Arbitration -UMDataStorage $true -Force
Now, verify that the mailboxes have been created and enabled. This can be done by using the following commands:
Get-Mailbox -Arbitration | Format-Table Name, ServerName, Database, AdminDisplayVersion, ProhibitSendQuota
To verify the audit log mailbox, run the below command.
Get-Mailbox -AuditLog | Format-Table Name, ServerName, Database, AdminDisplayVersion, ProhibitSendQuota
To Conclude
Removing and recreating the arbitration mailboxes should fix any issues and the Exchange Server should work fine. But what if this doesn’t work? There is a slight chance that the trouble with the Exchange Server is more on the database side. In such a case, you can restore a previous healthy backup. But this would mean that you will lose all your changes and content between the last backup and when the issue occurred.
You can use Stellar Repair for Exchange to avoid any data loss. Exchange Mailbox Recovery Software can recover database in case backup is failed, not available, or even you don’t have log files to recreate the entire mailbox database. It can recover database from failed server and mount it back on production server. You can also export recovered user mailboxes, disabled mailboxes, shared mailboxes, user archives, and public folders directly to another Exchange Server/database or Microsoft 365 tenant.
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