courier-mtaconfig: command not found

Have You tried accessing the binary with the full path?

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/courier-mtaconfig - from package: courier-mta

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