After a criminal is sentenced, he shall be sent to prison by the public security organ to which he belongs for execution. After officially leaving the team, the prison to which he belongs shall send a notice to his family within five days from the date of admission. The notice has a clear prison address, prison area and relevant regulations.
Writing to his family in prison will help him reform. You can write more letters to encourage him, but it is too much trouble to go to the post office. You can send a letter online, and just send it by post from home (e-mail).