Enitre letter canc. "ΝΑΥΠΑΚΤΟΣ*15.ΙΑΝ.64" fr. with 20l. sky-blue with vertically laid background (intense and very rare on cover) to Syros. Boxed "ΠΛΗΡ./ΑΝΕΠΑΡΚΗΣ" fr. on arrival with 20l. sky-blue and canc. "ΣΥΡΟΣ*19.ΙΑΝ.64". On reverse "ΑΘΗΝΑΙ" transit cancelation. Also oval postmans cachet "1" on arrival. Very rare. (Hellas 19a).