Welp, i have tried to mess around with the DNS on my Fedora 4 box, but I am in way over my head...
I know that the messages are there, as they show up in defer or deferred in /opt/zimbra/postfix-2.2.3/spool immediately after they get sent.
So as far as I understand it, I need to have the first DNS server in my resolv.conf file point to something that in turn points to the internal ip address first. That way, when postfix asks where "mail.example1.com" or "mail.example2.com" are located, it points them to 192.168.1.3 before it points them to the external ip.
Is that correct, or am I way off base? And if it is correct... (the million dollar question) how do I get it to work?
Fedora Core 4 has BIND installed by default, so I would imagine that I use that. However, the documentation/forums and information about DNS and Bind is pretty archaic, and I have been unable to find anyone that just needs to use a small DNS footprint that ONLY translates a host to an internal ip address.
I realize that this is a Zimbra forum and not a BIND forum... but I can't help but think that there are other users out there who have or will have a setup very similar to mine, so if it is a simple solution, posting it as "the answer" would be awesome. If it is more complex, then I'll keep on digging.