HI everybody,
I have been looking around and not finding anything that suits my problem I've been so crazed by this for a week now and I'd need some help.
First of all, let me apologize for my english, even though I am used to speak in English it is not my native language so please forgive the mistakes I might write.

So here's a bit of background to let you understand the environment in which I've been working.
I am a Network & System Tech in a city's IT service, i haven't been installing ANY of the servers I'll be talking about and none of them can be changed. That being said let's go.

For the schools' network we have a working Zimbra Server installed on an Ubuntu 12.04 Server, everything was fine.
For the city hall's network we used to have a Lotus Notes, and some people decided to change it and chose "bluemind" which is, well, quite crapy. Anyway, the bluemind server is pretty much working (installed on an Ubuntu Server as well).

My problem is, I can't seem to make those two servers exchange mails. I'v been looking around and trying solutions for over a week now, inserting MX or A (even CNAME) entries in our W2008R2 DNS/AD server. haven't changed anything.
Those servers are in the same network at our's (172.16.x.x) and can ping eachothers.
one is for a domain called TOWN.fr the other one is at schoolTOWN.fr, whenever zimbra tries to send a mail to TOWN.fr it is "timed out" on the EXTERNAL IP.
when I "dig TOWN.fr mx" I get the right answer (mail.TOWN.fr) in "Answer" but in the "additional section" I also get the external IP, which shouldn't appear (should it ?).
how could I make them exchange mails ?

I am sad to say I cannot change the BlueMind solution for a Zimbra, even though it is very poor compared to ZCS.
I have read the wiki page about split-DNS but that ain't it :
If you have a number of servers inside the firewall that need to use internal addresses to communicate to each other, you should consider setting up a full internal DNS server that can be authoritative for the whole domain. This example is not suitable for this task.
I'm not sure of what you could need to help me, but I am ready to fulfill any demand, screenshots and all.

If anything isn't clear, please ask me about details. I'm in such a mess now I have litterally NO idea where to go now.

thanks a lot for any help that could be provided.