Maddocks has written many articles on postal history, the majority reflecting his primary interest in the history of the Cameroons, particularly during the colonial period. He is the author of a monograph examining postal arrangements during the conquest of German Kamerun by the British and French during the First World War. His works also cover Nigeria, West Africa, Gambia, Zambia, German East and South West Africa, Togo, Ascension, St. Helena, Papua New Guinea, Jamaica and Barbados.