rblsmtpd: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/rblsmtpd - from package: ucspi-tcp-ipv6
/usr/bin/rblsmtpd - from package: ucspi-tcp

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