When a customer sends an email to a support email which runs on NeetoDesk then the email received by the customer won't have the ticket number in the subject. If we add the ticket number then the subject will change. Modifying the subject means that email will be part of a separate thread. This creates hassle. Hence NeetoDesk doesn't add ticket number to the subjects for the emails sent to the customers.
However emails sent to agents do contain ticket number.