After the war Estonia as Estonian Soviet Republic remained part of the Soviet Union. In January 1945 Ivangorod was administratively separated from Narva and was placed in the Leningrad Oblast in the Russian Soviet Federative Socialist Republic. In 1954 Ivangorod received city status. The river Narva was the border of the Estonian Soviet Republic. So this was also later the border of the again independent Estonia.
The postmark is something unclear, bur we see the indication НАРВА ЭСТ [NARVA EHST]
Here below a Christmas card, sent from Ivangorod, no longer part of Narva.
In the postmark we see the indication ИВАНГОРОД ЛЕНИН [IVANGOROD LENIN….], now in Leningrad Oblast, on the right bank of the Narva River. There are been disputes about the Estonian-Russian border. Acording the Treaty of Tartu (1920) and Estonia Ivangorod is Estonian. Now this Estonian Republic is restored, but the Russian Federation considers Estonia as the successor of the Estionian SSR with the Narva as border.