mhparam: 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/mhparam - from package: mailutils-mh
/usr/bin/mh/mhparam - from package: nmh

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

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