qmail-newaliases: 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/qmail-newaliases - from package: fastforward

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

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