In Japan, starting from mid-December, everybody starts sending nengajo 「年賀状」, New Year postcards for friends, relatives and colleagues. According to the tradition, nengajo should be delivered on the January 1st, and if the postcards are marked with the word nengajo and if they are posted on time (usually before December 25th), the Japan Post guarantees the delivery on time. Since almost every Japanese sends tens of these nengajo, the Post hires part-time workers to deliver all of them on the 1st day of the New Year.
The tradition of sending nengajo is very old, dating back in the Heian Period. It became a popular custom in 1871, when the postal service was founded. A couple of years later, the post started selling printed postcards and the number of nengajo grew so fast that in 1899 the post started handling the nengajo separately from the rest of the correspondence.
From 1950s, nengajo postcards printed with lottery numbers appeared, sold by the Ministry of Posts. They are still in use today, the lucky draw is held on January 15th and several billion are sold anually.
However, during the last years, the traditional postcards are replaced by electronic nengajo (delivered by e-mail or via mobile phone), made even with the lottery numbers, popular especially with the younger generation.
Of course, for persons with higher rank, teachers or business partners, the traditional postcards are still preferred…
I selected from Flickr several nengajo pictures, and if you want to see an electronic nengajo website, just search Google for 年賀状… :)