rspamd: 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/rspamd - from package: rspamd

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

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