These coaches are built between 1974 and 1976.
These coaches are initially used daily in block trains on long-distance connections. Such trains ran from Hamburg to Munich at night and mostly consisted of 10 to 12 of these cars.
It not only transported money, letters and parcels, but also unsorted consignments loaded in bags in larger node stations, sorted and distributed to the various postcode areas. Up to 8 postal workers carried out their nighttime sorting work and loading and unloading the mail bags and parcel pallets during the corresponding train stops.
These cars were designed as "high-security", whereby all doors and gates can only be locked from the inside. Additional external locking and sealing options made it "customs-ready" and thus also usable in international rail traffic.
It is equipped with an oil central combustion system with underfloor heating, a circulating air conditioning system, its own 24V power supply, a loudspeaker system, wardrobe, sink and toilet.
Sources: https://www.rheinmodellbahn.de/pages/eisenbahnepochen-iii-bis-v/rollmaterial-epoche-iv/reisezugwagen-epoche-iv.php, https://hellertal.startbilder.de/bild/deutschland~wagen~gepackwagen---bahnpostwagen/223715/schnellzug-bahnpostwagen-der-deutschen-bundespost-mrz-post-nr.html