 Within some of the destroyed suburbs , a limited postal system between various Robinson groups was established . Dawid Landau had served as a bodyguard to the courier of the Polish government in exile , Jan Karski , while Karski secretly entered the ghetto to gather information for a report on the extermination of Polish Jews by Nazi Germany for the Western allies , in 1943 . Later , Landau fought in both of the Warsaw uprising as part of <unk> Związek <unk> ( Jewish Military Union , <unk> ) and afterward decided to stay in the ruins . In his memoirs he reports that the post functioned through the use of empty electrical socket boxes . Various groups would leave notes for others informing them of who was alive and in hiding , news from the front that had been obtained , as well as requests for special forms of assistance . According to Landau , the most common pleas were for doctors or other forms of medical help . 
