Here is my setup. Hopefully somebody can give me some ideas on what to do or check.
Last night I installed Zimbra Open Source on a Fedora Core 6 vmware virtual machine (mail.mydomain.com) running on a Win XP Host.
I started with the Open Source binaries for Fedora Core 5.
My mail system sits behind a firewall/NAT router (a pfSense box) that is connected to the Internet. The internet connection has a dynamic IP address, and I update this address with dynamic DNS using an address at dyndns.com (mygateway.dnsalias.net). I set up port forwarding on the firewall/router for a bunch of ports to mail.mydomain.com, including http, https, smtp, ldap, etc.
mail.mydomain.com has a static address behind the firewall of 192.168.1.2.
The name server for mydomain.com does not support dynamic DNS, so I set up the name server entries so that the MX record points to mygateway.dnsalias.net that is updated automatically by my firewall/router. For mail.mydomain.com I added a CNAME record that points to the mygateway.dnsalias.net address. Using this setup I can ping mail.mydomain.com and a mail agent seems to be able to find mail.mydomain.com.
Installation of Zimbra all went fine, although I was warned that the MX record did not match the addresses of any of my interfaces (I guess this would always happen if you use a firewall/router). Nevertheless, I told it to just use mydomain.com and it completed without incident.
The system came up fine, and now I can create accounts, login as either user or administrator, set options, etc.
The problem I have is with mail. Mail is not successfully received or sent, whether local to local, local to remote, or remote to local. Looking at the administrative interface, the mail seems to be stuck in the Zimbra queues with a "Connection Timed Out" message to the gateway.dnsalias.net address (presumably the MX address for salkind.com). The firewall logs show no dropped packets, however.
When I send or receive a message, nothing appears in the Zimbra log file in /opt/zimbra/logs/zimbra.log. However, I do see the MTA agent log messages in /var/spool/messages, so I know the SMTP connection has happened. I can manually connect to the mail.mydomain.com SMTP server from outside the firewall using telnet on port 25.