mlpost: 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 Debian possible default full paths are:

/usr/bin/mlpost - from package: mlpost

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

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