stealthmail.gz: 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/share/doc/stealth/scripts/usr/bin/stealthmail.gz - from package: stealth

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

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