Ran into an issue with the service desk trying to use a new Mailbox server I was creating to be used as a backup server. Before I could get the DAG setup on the server we started getting tickets where new users could not access their mailboxes.
Looking into we discovered the Mailbox Database they were using were on the new server which because we kept getting pulled away from was not completely setup yet.
Of course just asking Service Desk to stop provisioning that database did not work .. they continued to do it.
So just run this command to Prevent the Database from being provisioned
Set-MailboxDatabase -Identity "Mailbox Database
To turn it back on re-run with $False.