mailfront: command not found

Have You tried accessing the binary with the full path?

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/sbin/mailfront - from package: mailfront

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