Appointy sends email reminders on every booking, cancellation or reschedule to alert administrators and staff about the changes in their schedule. These emails are important because sometimes you would not want a particular booking and want to cancel it instantly to keep it open for others.
Unfortunately, there is no way to stop it. However, you can create filters in your email to delete such emails as they arrive.
(Please note: Create filters on the "subject line" or "body content" and not on "From email")