Large official cover franked with 5 values of "ΕΛΛΗΝΙΚΗ ΔΙΟΙΚΗΣΙΣ" surcharge and cancelled with "ΕΛΛΗΝ. ΤΑΧΥΔΡΟΜΕΙΟΝ ΚΑΒΑΛΛΑΣ 1/14 ΙΟΥΛΙΟΥ 13". On reverse solemn declaration signed by Jean Proestakis for the authenticity of the stamps, verified by the French consular in Thessaloniki on 9/2/1914. Very important cover-document for the authenticity and circulation of that set ( Hellas 1, 7/8A, 8d, 9ad)