Yes, you can really send a letter to Jolin, it's all official!
2015 Jolin's birthday activity (Jolin's birthday is on September 15th)
Picture from Jolin's Fans Club Facebook
Jolin has been around for 16 years, she has released 13 albums, has lots of hits, has/had lots of endorsements too.
As a consequence there must be something related to her that you treasure the most. It can be something related to her endorsements, a present, or something rare like a cassette or limited edition singles for instance.
Take a picture of it, attach it to the form below, print it and write a message.
Jolin understands English, so there's no need to write your letter in Chinese if you don't speak it.
Address: 40148 台中市東區東光園路177巷33-1號／蔡依林國際歌友會收
Address translation: 40148 Taichung City East - East Road No. 177, Lane 33-1 / Jolin's International Fans Club
Source: Jolin's Fans Club Facebook