aliaslookup: 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/aliaslookup - from package: courier-mta

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

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