The offending stamps were printed for a group of Hitler enthusiasts through a service Deutsche Post offers to customize stamps, the Daily Mail (Britain) reported Thursday.
Hess was a deputy of Hitler. He was convicted of war crimes and sentenced to life in prison. He died in 1987.
"It runs in most cases without difficulty. Only with the Hess image did something go awry. We are sorry," Dirk Klasen of Deutsche Post said.
Klasen also said Deutsche Post would conduct a review of regulations in light of the Nazi stamps.