Arbitration mailboxes should be moved to another server to do this, run the command New-MoveRequest. To disable a Audit mailbox so that you can delete the mailbox database, run the command Get-Mailbox -AuditLog | Disable-Mailbox.
To disable a public folder mailbox so that you can delete the mailbox database, run the command Disable-Mailbox -PublicFolder.
To disable an archive mailbox so you can delete the mailbox database, run the command Disable-Mailbox -Archive. To disable a non-arbitration mailbox so that you can delete the mailbox database, run the command Disable-Mailbox. To get a list of all Audit mailboxes in this database, run the command Get-Mailbox -Database -AuditLog. To get a list of all arbitration mailboxes in this database, run the command Get-Mailbox -Database -Arbitration. To get a list of all public folder mailboxes in this database, run the command Get-Mailbox -Database -PublicFolder. To get a list of archive mailboxes in this database, run the command Get-Mailbox -Database -Archive. To get a list of all mailbox plans in this database, run the command Get-MailboxPlan.
To get a list of all mailboxes in this database, run the command Get-Mailbox -Database. This mailbox database contains one or more mailboxes, mailbox plans, archive mailboxes, public folder mailboxes or arbitration mailboxes, Audit mailboxes.