inmail-show: 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/inmail-show - from package: mh-book

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

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