1) Stop the “Microsoft Exchange Server Health Manager” service on all Exchange Server 2013 servers.
2) Open Exchange Management Shell and use following command to disable existing health mailboxes:
Get-Mailbox –Monitoring –resultsize unlimited | Disable-Mailbox
3) Go back to Active Directory users & computers, right click on domain and search for “HealthMailbox”
4) Delete the health mailbox user accounts.
5) Wait for AD replication or force AD replication.
6) Start the “Microsoft Exchange Server Health Manager” on all Exchange Server 2013 servers.