Relay SMTP - target not in DNS

[Trancemission]

Hi all,

I have the following problem which I cannot seem to be able to solve easily:

I have 2 mail servers, each accepting SMTP mail for 2 domains:

server1 handle email for server1.com
server2 handle email for server2.com

One of the servers [server2 which handles server2.com] will be taken of the public internet but will still be connected to our WAN via a private address and accessable from server1.

What I need to do is accept mail for server2.com on server1. server1 should then relay the mail should it be a server2.com address.


Looking through Exchange config I cannot seem to setup a 'static' route to route server2.com mail to a IP address.

I assume I can add the private address to the MX records of the domain - but I am not running Internal DNS [which I think maybe the answer - but will exchange know that the primary MX record is itself and then move on to the next?]

My ISP won't accept private addresses for DNS either [and I don't want to have to put that on External DNS]

Any help/advice appreciated.

Cheers
/mdt

Trancemission
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If it's logical, it'll work!