Email notification - Appointment

Hello,

I've created an appointment in CRM with a CRM-user in the Required field. (not a contact, a real CRM-user).
The appointent is present in the CRM-user calendar (Outllok and CRM) and all works fine.

But how can I set CRM options to send an email to the CRM-user email ? (Primary Email field for CRM user)

Thank you for your help.

Jerome