The United States Postal Service [USPS] in the late 80s - early 90s, confirmed that the Lubavitcher Rebbe received more pieces of mail each week than any other person in the entire country except for the President of the United States. What's amazing about this is that the US President has a whole team of people at the White House hired to open the mail being addressed to him, while the Rebbe personally opened 'each' letter addressed to him at 770.
Someone once suggested to the Rebbe that maybe he should at least use a machine to open these enormous piles of letters [arriving at 770 in huge mail bags each week from places all throughout the world], as the machine would speed up the process. The mail poured in each week from people of all walks of life, Jews, non-Jews, religious, non-religious, dignitaries, poor people, rich people, young people, old people, etc. Opening each letter by hand was very time consuming. And the Rebbe's schedule was much more busy than a normal person- the Rebbe barely slept, never took a vacation during his time as Rebbe, never left New York City during his time as Rebbe except on about two occasions to visit two different Lubavitch children's camps Upstate, and not one second was wasted.
And as the Lubavitch movement grew, so too did the mail grow. [First it was confirmed by the USPS in the 70s that the Rebbe received more mail than anyone in New York State except that going to the State Capitol, but by the late 80s and early 90s Lubavitch was exponentially larger than it had been in the 70s.]. Yet when asked why not use a machine, the Rebbe replied that some of the letters were sealed with the actual tears of people writing to him, and he said that he could not open a letter sealed with tears by using a machine.
This was the exceptional sensitivity of the Rebbe to every person.