In 1936 the British launched their 6th expedition to Mt Everest with the intent to reach the summit. Again, they followed the same route as the 33 & 35 expeditions and once again Gangtok was selected as the postal collection point. Similar to the 1935 marking, the expedition used a rectangular device with space for annotating the date or location.

   At some point early in the expd, the sub-postmaster at Gangtok had different ideas about the mail. The expd members become suspicious that the mail was not getting through since responses to questions and comments were not received in the incoming mail. During the return, the team reached Gangtok, Sikkim and paid a visit to the post office. The team questioned the sub-postmaster and searched the office where they discovered unforwarded letters. The regional Postmaster-General was informed and a postal investigation was initiated. During that investigation, several hundred letters were found. The sub-postmaster was subsequently convicted and sentenced to jail for the theft. This loss of letters and communication with home had to have resulted in great distress for families, friends and sponsors. In the end it was believed that over 500 letters were lost. Of that, 494 were recovered. These letters were each dated, numbered and initialed by the new sub-postmaster. The back of each cover was also marked with the seal of Sikkim and a label was attached explaining the delay before being forwarded without postage on to their final destination.