EV
then run the following commands one at a time. Once you have done that, remember to reboot (the reboot is critical)
Get-Mailbox -Arbitration | disable-mailbox -Arbitration -DisableArbitrationMailboxWithOABsAllow –DisableLastArbitrationMailboxAllowed
Get-Mailbox -AuditLog | Disable-Mailbox
Get-Mailbox -Monitoring | Disable-Mailbox