milter-regex: 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 CentOS possible default full paths are:

/usr/sbin/milter-regex - from package: milter-regex

You may install the required package with command yum install {package}

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