Hello ZhangHuangbin and thanks a lot for your quick reply.
I have the two domains added for testing.
I unnderstand that the mails between the domains added are delivered locally.
The result for "nslookup my-domain.com" is:
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
Name: my-domain.com
Address: 212.142.144.10
Name: my-domanin.com
Address: 212.142.144.9
I have solved the prolblem adding the 2 google dns directions on /etc/resolv.conf
But the main problem (send mail to outside) is still ocurring.
When I send a mail to outside I receive this answer:
"<maildir@maildomain.com>: host mail.domain.es[194.30.0.71] said: 550 5.1.8
<myiredmailuser@myiredmaildomain.com>: Sender address rejected: Domain not found (in
reply to RCPT TO command)"