It worked fine in 1.6 and 1.7.x. If I remember correctly it was removed in 1.8 you should use %{response}.
Q: Help %{message} isn't working!
A: %{message} was removed as a
valid template code a while ago, Did you mean to use %{response} or
perhaps %{ticket.thread.original}? Go to Admin panel -> Emails ->
Templates and in your email template add one of them. Keep in mind that
if you use %{ticket.thread.original} that this will result in the
original message every time that template is triggered.
source: tmib.net - osTicket 1.8.x FAQ
