There is a custom called ‘Nengajyo（年賀状）’ at new year in Japan. Write “年賀状” on the face of the postcard and put it in the post, it will be delivered to the other’s house on the morning of January 1.
Japanese people communicate with each other and their friends acquaintance who have been unable to meet easily through Nengajyo. Some people keep friends only by exchange of Nengajyo.
However, this old-fashioned interaction is also getting ruined in recent years, because we can be easily contacted by SNS etc.