mailrm: 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/mailrm - from package: masqmail

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

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