greylistd-setup-exim4: 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/greylistd-setup-exim4 - from package: greylistd

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

Error in other languages:
greylistd-setup-exim4: bevel nie gevind nie
greylistd-setup-exim4: comandă negăsită
greylistd-setup-exim4: comando não encontrado
greylistd-setup-exim4: commande introuvable
greylistd-setup-exim4: command not found
greylistd-setup-exim4: käsku ei ole
greylistd-setup-exim4: không tìm thấy lệnh
greylistd-setup-exim4: komanda nerasta
greylistd-setup-exim4: Kommando nicht gefunden.
greylistd-setup-exim4: kommandot finns inte
greylistd-setup-exim4: komut yok
greylistd-setup-exim4: nie znaleziono polecenia
greylistd-setup-exim4: níor aimsíodh an t-ordú
greylistd-setup-exim4: no se encontró la orden
greylistd-setup-exim4: no s'ha trobat l'ordre
greylistd-setup-exim4: opdracht niet gevonden
greylistd-setup-exim4: parancs nem található
greylistd-setup-exim4: perintah tidak ditemukan
greylistd-setup-exim4: príkaz nenájdený
greylistd-setup-exim4: příkaz nenalezen
greylistd-setup-exim4: команда не найдена
greylistd-setup-exim4: командата не е открита
greylistd-setup-exim4: 命令找不到
greylistd-setup-exim4: コマンドが見つかりません