mailpatch: 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/bin/mailpatch - from package: mailagent

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

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