mimedefang-multiplexor: 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/mimedefang-multiplexor - from package: mimedefang

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

On Debian possible default full paths are:

/usr/bin/mimedefang-multiplexor - from package: mimedefang

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

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