Setup email notifications for moderators

Please can you provide instructions for how to set up email notifications for moderators. I have provided an email address in categories/general/notifications.

If I set 'email on page load' in general/maintenance the user gets 'Could not instantiate mail function.' when submitting a post.

I'd be happy to create a cronjob to email moderators with notifications but I don't know what command to use (I'm very new to this).

Thanks, Kerstyn