I have enabled "Contact Notifications" -> "Receiving a new Ticket". My understanding is that this will send an acknowledgement email to the contact. Unfortunately, emails are not being sent to the contact on ticket creation. A look at history suggests that this is not being triggered either. 

"Contact Notifications" -> "Closing a Ticket" and "Department Notifications" -> "Creating a new Ticket" seem to be working fine though. Only "Contact Notifications" -> "Receiving a new Ticket" seems to be having a problem