update-exim4defaults: 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/update-exim4defaults - from package: exim4-config

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

Error in other languages:
update-exim4defaults: bevel nie gevind nie
update-exim4defaults: comandă negăsită
update-exim4defaults: comando não encontrado
update-exim4defaults: commande introuvable
update-exim4defaults: command not found
update-exim4defaults: käsku ei ole
update-exim4defaults: không tìm thấy lệnh
update-exim4defaults: komanda nerasta
update-exim4defaults: Kommando nicht gefunden.
update-exim4defaults: kommandot finns inte
update-exim4defaults: komut yok
update-exim4defaults: nie znaleziono polecenia
update-exim4defaults: níor aimsíodh an t-ordú
update-exim4defaults: no se encontró la orden
update-exim4defaults: no s'ha trobat l'ordre
update-exim4defaults: opdracht niet gevonden
update-exim4defaults: parancs nem található
update-exim4defaults: perintah tidak ditemukan
update-exim4defaults: príkaz nenájdený
update-exim4defaults: příkaz nenalezen
update-exim4defaults: команда не найдена
update-exim4defaults: командата не е открита
update-exim4defaults: 命令找不到
update-exim4defaults: コマンドが見つかりません