qmail-rspawn: 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

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

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