core_server: 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/core_server - from package: spambayes

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

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