This modern German postmark indicates that the letter was presented at the post office counter in Kieselbronn, Baden-Wuerttemberg. Fortunately, the stamp did not receive a second, disfiguring cancel after it was sent to the "Briefzentrum 76" (district letter processing center) in Karlsruhe.
As modern Germany collectors know, the vast majority of stamps receive a Briefzentrum cancel. From Wikipedia, "Before 1993, there were more than 1000 centers for the processing of letters. With the introduction of the new postal codes in Germany, 83 different district centers were built between 1994 and 1998...(Today) there are 82 district processing centers."
Population of Kieselbronn is 3010 (12.31.18 Wikipedia).