postal: 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/postal - from package: postal

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

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