qmtpfront-qmail: 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/sbin/qmtpfront-qmail - from package: mailfront

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

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