Running Zimbra behind DNAT

[Baylink]

I will be running my Zimbra box inside my NAT/firewall boundary, on an RFC 1918 address.

In my public DNS, I plan to call it mx1.example.com, which will resolve to the IP of my firewall, which in turn will forward 25 and 110 to the box inside.

In my private DNS, and on the physical box, the name of the ethernet interface is benjamin.example.com.

So, my question is (and yes, I looked here) is this:

Where else do I have to put in an FQDN, and what should I use there? I gather the answer is "into ZImbra" and "into postfix", but even given that, I'm not sure which lies to tell to whom... :-)

(The machine is OpenSUSE 10.2, if that matters for this, and I'm running real internal DNS.)

[Baylink]

You can ignore that last sentence. Since I find -- after doing the entire OS install -- that I've misread the Sunset Binaries page, and that OpenSUSE 10 is not supported for NE, here I go again, off to grab a CentOS 5 install image.