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

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

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