ali: 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/ali - from package: mailutils-mh
/usr/bin/mh/ali - from package: nmh

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

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