GeneTE:
My voltage divider limits the current to ~10mA. So, I don't need any extra protection even if the input voltage is a little more then 5.5V. Right?
Wrong.
So you didn't read (or understand) post#10.
The current through the voltage divider is irrelevant to the Arduino.
It just burns power in the divider.
What matters is the current into the Arduino pin protection diodes.
Leo..