authtest: 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/authtest - from package: courier-authlib

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

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