Problem with multi-homing

[Thierry]

I have a firewall (RH 6.2) with 3 NICs:
- one permanent connection to the Internet (A.B.C.237)
- one for DMZ (10.1.1.0)
- one for private LAN

Primary DNS & Mail server is on the DMZ and on the same server (running
RedHat 6.2 at 10.1.1.10)
Secondary DNS & Web server is on the same server (running NT 4 at 10.1.1.11)

Although these 2 servers have private IP addresses (10.1.1.10 and
10.1.1.11), I'm using IPMASQ on the firewall to redirect packets to those
servers. This works perfectly when pinging A.B.C.225 and A.B.C.226.

For virtual-hosting mail on RH6.2 (10.1.1.10), I'm using vpop and multiple
private IP addresses using "ifconfig eth0:x" on 1 NIC.
For virtual-hosting ftp on NT4 (10.1.1.11), I'm binding multiple private IP
addresses on 1 NIC.

Now, my question:
how (from the Internet) can I access the server mail.domain1.com (declared
at 10.1.1.50 in my DNS) or mail.domain2.com (declared at 10.1.1.51) without
having an official IP address for each virtual server ?

Thanks,
Thierry.

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