Hintertreppe (1921)

A crippled mailman is in love with a maid who lives in the same building he does in one of the city's poor neighborhoods. She, however, is in love with a wealthy, handsome young man. Desperate to win her love, he begins to intercept love letters they send to each other and replaces them with his own messages, which each thinks is from the other. His plan seems to be succeeding, but then something happens that bring tragic results to them all.