Change network for zimbra

[kilg]

hi
I'm going to deploy zimbra FOSS on rhel5 x32_64
at first, I plan to locate server in my local network(192.168.0.0\24) and make DNAT from gateway(192.168.0.254) to zimbra server(192.168.0.1).
In iptables I'll write:

-A PREROUTING -d my_wan_ip -p tcp -m tcp --dport 25 -j DNAT --to-destination 192.168.0.1:25

Will this firewall's rule is enough?
The same way I specify in /etc/hosts:
192.168.0.1 mail1.mydomain.loc mail1
After installing zimbra, I rename mydomain.loc in mydomain.com.
Will zimbra works correct in this way? Or zimbra will troubles with sending and receiving mail?
I described my first step.

Then I going to make this zimbra server gateway in my local network.
Local interface will be same(192.168.0.1) and it will extern IP, for example, xx.xx.xx.xx
Should I rewtite /etc/hosts to
xx.xx.xx.xx mail1.mydomain.com mail1 ? Will its enough?
How many troubles may I get?