Gabriele's fix will only work for two recipients. I modified the smartd-runner script as follows for additional recipients as I needed three:
#run-parts --report --lsbsysinit --arg=$tmp --arg="$1" \ # --arg="$2" --arg="$3" -- /etc/smartmontools/run.d subject_opt="${1}" shift subject="${1}" shift recipients="${@}" run-parts --report --lsbsysinit --arg=$tmp --arg="${subject_opt}" \ --arg="${subject}" --arg="${recipients}" -- /etc/smartmontools/run.d