amavisd-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 Debian possible default full paths are:

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

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

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