If he gets so many emails that his gmail is overflowing, does he really look at all of them in the first place.

While motion detection does not work well outside, unless you're using the crappiest NVR, things like leafs and shadows should not trigger motion alerts.

Now, leaves blowing into the camera CCD, blocking FOV, or sand/snow blowing at night making infrared light up like a blizzard, that's a different story.

I tried to use my front door camera's motion detection to trigger lights (at night) and music at portico. After that failure, I've installed outdoor rated PIR (3-4 years ago), and except for very hot days, where body temperature is below ambient one, I have not had any issues or false alarms.