clamav-milter: 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/clamav-milter - from package: clamav-milter

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

On Debian possible default full paths are:

/usr/sbin/clamav-milter - from package: clamav-milter
/usr/lib/debug/usr/sbin/clamav-milter - from package: clamav-dbg

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

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