mysend: 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/share/doc/mh-book/examples/mh/bin/mysend - from package: mh-book

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

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