Saludos a tod@s

Por favor me pueden dar una pista de como resolver este mensaje de error

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

soporte@ecuatoriano.ec: host mx1.emailsrvr.com[66.216.118.113]
said: 550 5.1.0 nada@secretaria.ec: Sender address rejected: User
unknown in relay recipient table (in reply to RCPT TO command)

Tengo instalado un servidor de correo postfix sobre Centos 5, cuando intento enviar correo desde el dominio secretaria.ec a una cuenta de ecuatoriano.ec me da este error.

Gracias por su colaboración.