postsuper: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/postsuper - from package: postfix

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/postsuper - from package: postfix

You may install the required package with command apt-get install {package}

Error in other languages:
postsuper: bevel nie gevind nie
postsuper: comandă negăsită
postsuper: comando não encontrado
postsuper: commande introuvable
postsuper: command not found
postsuper: käsku ei ole
postsuper: không tìm thấy lệnh
postsuper: komanda nerasta
postsuper: Kommando nicht gefunden.
postsuper: kommandot finns inte
postsuper: komut yok
postsuper: nie znaleziono polecenia
postsuper: níor aimsíodh an t-ordú
postsuper: no se encontró la orden
postsuper: no s'ha trobat l'ordre
postsuper: opdracht niet gevonden
postsuper: parancs nem található
postsuper: perintah tidak ditemukan
postsuper: príkaz nenájdený
postsuper: příkaz nenalezen
postsuper: команда не найдена
postsuper: командата не е открита
postsuper: 命令找不到
postsuper: コマンドが見つかりません