I already sent an email to firstname.lastname@example.org
but I get this message back:
Mail Delivery System MAILER-DAEMON@networkclub.com.br for me
show 10:06 (4 minutos atrás)
This is the mail system at host networkclub.com.br.
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 postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
<email@example.com> (expanded from
<firstname.lastname@example.org>): unknown user: "networkclub.com.br/cleber/"
Final-Recipient: rfc822; email@example.com
Diagnostic-Code: X-Postfix; unknown user: "networkclub.com.br/cleber/"