The Error: Couldn’t disable the arbitration mailbox because it is associated with existing recipients for which membership restriction of approval is required or the moderation feature is enabled. Please disable the approval feature on those recipients before performing this operation.

Scenario:  You receive the following error when trying to disable/remove an arbitration mailbox:

Couldn’t disable the arbitration mailbox because it is associated with existing recipients for which membership restriction of approval is required or the moderation feature is enabled. Please disable the approval feature on those recipients before performing this operation.

Solution:  Locate the distribution groups that are using this arbitration mailbox.  You will be able to transfer the arbitration mailbox used by the distribution groups if you have another.

Get-distributiongroup  | Select Name, ArbitrationMailbox

OR

Get-distributionGroup | Where ArbitationMailbox -like “Domain.Com/Users/SystemMailbox{149831f20381-30d4-ed31-1345defe2313”

You can use the opposite to set it to the new Arbitation mailbox:

set-distributiongroup -identity “name of Distribution Group” -arbitrationmailbox “name of Arbitration Mailbox”