Hi anonymous user
Any progress here, have you succeed removing the default mailbox database now?
We could refer to the article here introduced the details about Move arbitration mailboxes in Exchange Server
In addition, sometimes we may encounter the issue failed to remove database: This mailbox database contains one or more mailboxes, mailbox plans, archive mailboxes, public folder mailboxes or arbitration mailboxes.
Executing the following cmdlets does not reveal any other types of mailboxes that reside in the database, then remove them or disable them:
Get-Mailbox -Database "test database" -ResultSize Unlimited | New-MoveRequest -TargetDatabase "database"
Get-Mailbox | Where ArchiveDatabase -eq "test database" | New-MoveRequest -ArchiveOnly -ArchiveTargetDatabase "database"
Get-Mailbox -Database "test database" -Arbitration | New-MoveRequest -TargetDatabase "database"
Get-Mailbox -Database "test database" -PublicFolder | New-MoveRequest -TargetDatabase " Database"
Get-Mailbox -Database "test database" -AuditLog | New-MoveRequest -TargetDatabase "Mailbox Database 1"
Get-Mailbox -Database "test database" -Monitoring | Disable-Mailbox -Confirm:$false
And if you still have issue removing the database after performing the steps above, consider using ADSIEdit to finfish it.
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