smd-loop: 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/smd-loop - from package: syncmaildir

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

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