libdkimtest: 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/libdkimtest - from package: libdkim-dev

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

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