How to prevent the system from sending ad email on Appointment's status change.

Hi everyone,

I switched from version 1.7.X to 1.9.4 and this feature seems to be changed.
In a nutshell, as an Admin of the booking system, I am free to change the status of the appointment from Confirmed to Paid, for example.

I need that the system sends an email to the customer only once, when the appointment is requested from the front end.

Currently the customer receives an email every time I change status of his appointment.
Is there a way to disable it?

Thank you