border mx

[Andrew Pantyukhin]

On 12/20/06, Alexei <root at sovetnik.org> wrote:
> Hello, freebsd-net.
>
> I'm going to build some mail system, so I need some advice.
> There is a network with a 'MS Exchange' as a mail server and
> 'someintdomain' as an internal mail domain. I also have an internet
> domain, for example 'mydomain.com'. There is a freebsd box as a
> gateway for my network, and 'MX' record of 'mydomain.com' will point
> on it's address.
> What I need:
>
> - when someone sends mail from internet to 'vasya at mydomain.com', my gw
> replaces vasya at mydomain.com with 'vasya at someintdomain' and sends it to
> Exchange server
> - when someone from my internal network (vasya at myintdomain) sends mail
> to some internet mail address (ie sends it to ms exchange server and
> exchange sends it to gw), my gw replaces 'From:' and 'Reply-to:'
> fields vasya at someintdomain -> vasya at mydomain.com
>
> Is that real? How can I realise this system? Or, maybe, there is some
> other way to get the result I need?
>
> PS: 'Exchange' server has 'grey' address (192.168.0.0/16) and I don't
> want allow him connect to the internet directly.
> PPS: Sorry, if this question is not suitable for this maillist, so
> advise me please where to ask.

I would redirect you to another place but most of
what you want is discussed in almost any mailserver's
manual, even that of Exchange, I'm sure.

A couple of pointers:

1) You are right in not wanting to directly connect a
   192.168.x.x address to the internet, your ISP
   wouldn't appreciate that ;)

2) Spamwise, the gw mx should be able to tell a valid
   (internal) address from an invalid one. There are
   different approaches, from importing aliases db
   from Exchange at regular intervals to verifying
   addresses over SMTP and what not.

Good luck!