sa-compile: 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/bin/sa-compile - from package: spamassassin

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

On Debian possible default full paths are:

/usr/bin/sa-compile - from package: sa-compile

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

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