mlmmj-send: 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/bin/mlmmj-send - from package: mlmmj

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

On Debian possible default full paths are:

/usr/bin/mlmmj-send - from package: mlmmj

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

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