mdel: 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/mdel - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mdel - from package: mtools

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

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