qail: 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/bin/qail - from package: qmail
/var/lib/qmail/bin/qail - from package: qmail

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

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