Ok, thanks.
Finally we didn't the backup and restore because it didn't work. But our hostname and zmhostname is not smtp.obertic.com, it's obertic.dedi.acens.net as old server. This entry was added by our provider to their dns in the first installation on old server, about one year ago. I've asked for change this entry to the new ip, but it hasn't still taken effect.
Then, my conclusions are: Zimbra is not receiving mails because my hostname and zimbra server name aren't smtp.obertic.com although there's an entry with new ip, and because obertic.dedi.acens.net (the real hostname machine and server name) it's still directing the traffic to the old server ip by our provider dns.
This is the link to the old server installation thread in this forum:
[SOLVED] Installing on hosting dedicated server