dkimproxy-sign: 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/dkimproxy-sign - from package: libmail-dkim-perl

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

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