rmm: 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/mu-mh/rmm - from package: mailutils-mh
/usr/bin/mh/rmm - from package: nmh

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

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