Hey Baylink,
Sorry you didn't get any love earlier. . .been a long week for me. Just wiped out your dupe thread. . .
As to your domain issues, first of all, nobody with any sense is going to try to dissuade you from hiding behind a DNAT/SNAT box. . .I share your opinion that anything else, if not suicide, is at least very poor practice. This is where the split-DNS stuff you will find all over the forum comes into play. Basically, you load bind or bind9 on your Zimbra box, or else you have an internal DNS on another box in your DMZ subnet, and that provides your Zimbra box with (dare I call it) "self-resolution" INCLUDING MX RECORD to the internal (real) IP of your box on the DMZ. Of course, the rest of the world resolves your mailserver to the public IP via DNS that is "out there;" only your DMZ shows the internal DNS.
Second, there is an irritating little element in the install script where it implies to any normal reader (we've probably all been thru this) that it wants your FQDN, when what you should really put in is just your hostname (benjamin in your case?), and in other places just the domain (vicimarketing.com) and never both together.
This wiki, while written for a Ubuntu installation, goes over some of these concepts in greater detail and may be helpful to you since you already understand basic Linux concepts.
If further questions come out as you play with this, just post back; despite how quiet it looks this forum really is the place to come for answers.