spamass-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/spamass-milter - from package: spamass-milter

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

On Debian possible default full paths are:

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

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

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