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Exchange 2013 : What is an arbitration mailbox? / Unable to Decommission an Exchange server. [Solved]

When Decommissioning an old Exchange server you may receive this error massage :

 

Configuring Prerequisites COMPLETED

Prerequisite Analysis FAILED

Uninstall can’t continue.

Errors:

This mailbox database contains one or more mailboxes, mailbox plans, archive mailboxes, public folder mailboxes or arbitration 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 mailbox plans in this database, run the command Get-MailboxPlan. To get a list of archive mailboxes in this database, run the command Get-Mailbox -Database <Database ID> -Archive. To get a list of all public folder mailboxes in this database, run the command Get-Mailbox -Database <Database ID> –PublicFolder. To get a list of all arbitration mailboxes in this database, run the command Get-Mailbox -Database <Database ID> –Arbitration. To disable a non-arbitration mailbox so that you can delete the mailbox database, run the command Disable-Mailbox <Mailbox ID>. To disable an archive mailbox so you can delete the mailbox database, run the command Disable-Mailbox <Mailbox ID> -Archive. To disable a public folder mailbox so that you can delete the mailbox database, run the command Disable-Mailbox <Mailbox ID> -PublicFolder. Arbitration mailboxes should be moved to another server; to do this, run the command New-MoveRequest <parameters>. If this is the last server in the organization, run the command Disable-Mailbox <Mailbox ID> -Arbitration -DisableLastArbitrationMailboxAllowed to disable the arbitration mailbox. Mailbox plans should be moved to another server; to do this, run the command Set-MailboxPlan <MailboxPlan ID> -Database <Database ID>.

Most of the time, you receive this error because of the Arbitration mailboxes.

 

What is an arbitration mailbox?

From Technet :

The arbitration mailbox is used to store the original message that’s awaiting approval. By default, one arbitration mailbox is created for moderated transport during setup. It’s used for all moderated recipients. You can add additional arbitration mailboxes for load balancing purposes. If you’re using multiple arbitration mailboxes, you need to specify which mailbox to use for each moderated recipient. mailbox is used to store the original message that’s awaiting approval. By default, one arbitration mailbox is created for moderated transport during setup. It’s used for all moderated recipients. You can add additional arbitration mailboxes for load balancing purposes. If you’re using multiple arbitration mailboxes, you need to specify which mailbox to use for each moderated recipient.

A lot more information about using arbitration mailboxes can be found here: Understanding Moderated Transport

In short, arbitration mailboxes are where messages awaiting moderation are stored, as well as information about moderator decisions are kept.

 

These are the 2 most common situation where you need to use arbitration mailboxes.

1. I deleted my arbitration accounts from my AD

This isn’t really all that bad, you need to rerun the AD preparation steps from the 2013 media.

Setup.com /PrepareAD /IAcceptExchangeServerLicenseTerms

or

.\Setup /PrepareAD /IAcceptExchangeServerLicenseTerms

2. I am trying to remove Exchange 2013, or a database, or the Mailbox role and am being told there are arbitration mailboxes preventing me from continuing

When you try to remove the first DB in Exchange 2013, there are a few arbitration mailboxes that will prevent database deletion. You have the choice of moving, removing, or mail-disable these mailboxes. Since you cannot see these in the Exchange Admin Center, you need to launch Exchange Management Shell (EMS)

Get-Mailbox -Arbitration

This will list the arbitration mailboxes.

Get-Mailbox -Arbitration -Database DataBase1

Use the –Database option, to narrow it down to a specific database.

Once you have your “get” command returning the correct list of mailboxes, it’s time to move, disable or remove them. Disabling the last arbitration mailbox is not allowed, so I recommend moving them as the first preference here.

Move:

Get-Mailbox -Arbitration -Database DataBase1| New-MoveRequest -TargetDatabase DataBase2

Disable:

Get-Mailbox -Arbitration -Database DataBase1| Disable-Mailbox -Arbitration

Remove:

Get-Mailbox -Arbitration -Database DataBase1| Remove-Mailbox -Arbitration -RemoveLastArbitrationMailboxAllowed