According to a referencelist - dated 1927 - from the German company Mix & Genest AG, Abteilung Rohrpost und Förderanlagen in Berlin-Schöneberg, the Italian city of Naples had access to a Pneumatic City Mail system with ten stations and a tube length of 17 kilometers.
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Letter sent in Naples at April 5th, 1928. It arrived the next day in Milan where it was stamped again at the backside.
Envelop sent from Napels to Milan.