dkim-milter.py: 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/dkim-milter.py - from package: dkim-milter-python

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

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