This can happen if you have users type mailbox without belonging to mailbox database To find those users, execute powershell command : Get-Mailbox -arbitration | Select Name,
Month: April 2017
Configure exchange 2013 CAS High AvailabilityConfigure exchange 2013 CAS High Availability
From exchange 2013 Microsoft drop the cas arrey function as the mailbox client connect through HTTPS only, achieving High Availability with CAS server will be done with some other form