Erro de email

Boa Noite Caros

Sempre que o meu cliente envia um email, vem um erro

Hi. This is the qmail-send program at plesk-pri.acs.ao.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<'antonio.aguiar@princesa.co.ao'>:
Sorry, I couldn't find any host named princesa.co.ao'. (#5.1.2)

fixed ip the domain in file /etc/hosts release test