“The Jews, who were in Susa, gathered on the thirteenth day and on the fourteenth day. They rested on the fifteenth day of Adar, making that a day of feasting and gladness. Therefore the Jews of the villages, who live in the open towns, hold the fourteenth day of the month of Adar as a day for gladness and feasting and holiday-making. This is a day on which they send gifts of food to one another.”
There was a difference between the Jews in Susa and those in the various villages. Since the Jews in the city of Susa defended themselves for 2 days, they did not celebrate until the 15th or Adar instead of the 14th as the rest of the provinces. During this day of celebration they sent gifts of food to one another.
Eugene Finnegan Bible Project 