Is there an option in Orchestrator user preferences to disable Dashboard emails for specified users? The users that do not wish to receive mails from Orchestrator had unsubscribed from email Notification/Alerts (from My Profile settings page) but they are still receiving Orchestrator dashboard mails.
This is an issue for many; removing email from user profile makes things easier but this will affect those who wish to receive at least job fault notifications.
I found DailyAlertMailJobCron in webconfig. Try adding a cron expression for once a year or based on your requirements.