DO NOT send mail anywhere that is addressed "Any Soldier" or "Recovering Serviceman". The postal service will not deliver it and if it slips through, no military facility will accept or deliver it.
They have a program through official channels that pre-screens the mail to ensure nothing harmful or inappropriate gets through. Unfortunately we live in a world that has some not-so-nice people in it- people that have agendas and may not wish our servicemen well. This program protects them while allowing well-wishers the opportunity to get mail to a serviceman.