esmtpd: 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/sbin/esmtpd - from package: courier-mta

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

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