My plain user experience is that it happens because of sensor static.
Especially with higher gains the sensor is very poor, and causes so much fluctuation in the picture that Motion Detect considers this as an event.
Possible workarounds: lower the motion tracking sensitivity: Not percentage, but sensitivity. Second, lower gain to reduce static. Third use denoise and other picture parameters to make it less noisy. Fourth: use stronger lighting and/or exposure mode (connected to max gain).
Also if you set up your own Event, and click *off* the mydlink.com settings page email notification, it should skip the Log messages. I think the mydlink.com event is somehow different from the camera's setup page events. If you have only your own event, and not the mydlink.com email on, it will send what you want and not the logs.
Too bad the sensor is that noisy. Even in very good light it gives multiple times worse picture than for eg in mobile phones.