mailhelp: 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/mailhelp - from package: mailagent

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

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