Military post offices on the Salolica front. The Serbian High scool at Volos. Registered cover fr. with 6x5l. + 2x10l. "ET" Greek stamps and posted from "ΒΟΛΟΣ*26.ΔΕΚΕ.17" with Greek censorship tape "ΕΛΛΗΝΙΚΗ ΛΟΓΟΚΡΙΣΙΑ" and French "OUVERT par lAUTORITE MILITAIRE*303" and tape "CONTROLE POSTAL MILITAIRE", arr. "LAUSANNE*18.II.18". On reverse Serbian Unit marking.