lookup.pl.gz: 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/share/doc/mailagent/examples/rc/sbin/lookup.pl.gz - from package: mailagent

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

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