DNS ERROR resolving MX for mail.domain.com

[webman]

Is the other server running Postfix as it's MTA? If so, you can add this to /etc/postfix/transport:

my-zimbra-domain.com    smtp:192.0.0.121

Then run this once it's saved:

postmap /etc/postfix/transport

I'm not personally familiar with any other mail servers except Postfix, but someone else should be able to help providing you supply us with the necessary information.

[dwmtractor]

Originally Posted by csoliss

this is my firewall configuration

port 25 Protocol: SMTP
incoming: from any to 192.0.0.121(zimbra server IP) 192.0.0.151 (other mail server)
outcoming from any to any

NOTE: the other mail server have other domain.

You may have done this but not fully explained it here, I don't know. What I see missing from your config descriptions is that you must have a different published PUBLIC ip address for each of your mail servers (since there are two) and for each, you have to have a Destination Network Address Translation (DNAT) rule that accepts traffic from to the public ip and translates its destination to the appropriate private IP.

Then, if you ever want to do externally-authenticated users, you also need an SNAT (Source NAT) rule that takes outgoing traffic from your Zimbra server and translates its source to the public IP of your mailserver; otherwise it'll be sourced as the primary IP of your firewall which will result in RDNS lookup failures and failure to authenticate for external clients.