Sending New Year’s cards to relatives, friends, teachers, classmates, and co-workers is a very important custom in Japan. The cards are supposed to be delivered after January 1st. (Never before!)
Japanese post offices accept New Year’s cards from mid-December, but they don’t deliver them until New Year’s Day. So, be sure to write ‘nenga’ under the stamp so that postal workers can distinguish them from regular mail.
Another important part of the etiquette is not to send a New Year’s card to a family in mourning. You might receive cards from people who are in mourning before December, notifying you that they don’t take New Year’s cards that year.
The Ministry of Postal Service and Telecommunications in Japan issues prepaid New Year’s postcards with lottery numbers every year. These cards are the kind most commonly used by Japanese people. The lottery’s winning numbers are picked in mid-January. The prizes aren’t money, but are various household goods, such as cameras, electronics, stamps, and so on.
It’s a tradition for Japanese people to write New Year’s cards during December, but it can be time consuming.
JICA