couriermlm: 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/couriermlm - from package: courier-mlm

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

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