I am having trouble setting up the split DNS - Zimbra behind a firewall configuration.

Problem = All outgoing email errors - domain loops back to myself.

I have tried to follow the WIKI on split DNS and various post on this - but still no luck.

I have a CentOS 5.3 Firewall box - basic loaded with Webmin.

Right now the Firewall only forwards ports 25 and 7025 to the Zimbra server.

I have a CentOS 5.3 Zimbra Server (open source version)

I am able to receive email to the domain without a problem.

DNS settings at godaddy:
Point to firewall external IP
MX record points to mail.domain.net

firewall FQDN:

Zimbra server FQDN:

firewall DNS has no entries for the Zimbra server, just Default DNS config, no entries the HOSTS file for the Zimbra Server, the Resolve file point to the two external DNS servers from my ISP.

Zimbra server:

The Resolv.conf file on the Zimbra server points to itself for resolution then the firewall server.

Zimbra server:

Host file:
has just the three lines:
search mail.domain.net (local host FQDN) mail.domain.net mail

Has CentOS default DNS configuration with one additional record for the Zimbra server:

@ IN SOA mail.domain.net. admin.domain.net.
serial, refresh.....
@ IN NS mail.domain.net.
IN MX 10 mail.domain.net.
mail.domain.net. IN A

Zimbra settings:

MTA - have tried localhost, mail.domain.net, - with and without DNS lookup. In no combination have I been able to send out email.

Any one have some suggestions.