Esther 9:19 (ESV)

19 Therefore the Jews of the villages, who live in the rural towns, hold the fourteenth day of the month of Adar as a day for gladness and feasting, as a holiday, and as a day on which they send gifts of food to one another.

It became an ongoing custom for rural Jews (those living outside of fortified cities such as Susa) to begin their Purim celebrations on the fourteenth of Adar. On this day, they would also give presents to each other (a custom from which the poor would also benefit; see Nehemiah 8:10).