comp: 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/mu-mh/comp - from package: mailutils-mh
/usr/bin/mh/comp - from package: nmh

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

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