Multiple mail servers on virtual domains

[Doron Shikmoni <doron () isoc org il>]

Hello,

I'm setting up a mail server in a firewalled environment.
This server is sitting behind a packet-based firewall,
on a 2nd border line which includes application proxy
gateways (for mail and HTTP).

This server should serve a multitude of populations. Hence,
it should serve multiple virtual domain (highly desirable,
from one physical Unix host).

So far there's nothing special. However, I would need these
virtual domains to be served different mail repositories
(i.e., johndoe () domain1 our net should be a different user
from johndoe () domain2 out net). This (I think) rules out
the idea of running one mail server with a few v-domains.

I've come up with an idea of running multiple instances
of a complete mail server (say, Netscape Messaging or what).
This poses two issues:

1. Passing the various port-25 connections to the various servers.
   I trust this can be done by having each server listen to
   a different port (say, 20025, 20026, 20027 and so on); and have
   something like TIS plug-gw loop each virtual host's port 25
   into a different server. (As in: 10.0.0.1:25 to 127.0.0.1:20025,
   10.0.0.2:25 to 127.0.0.1:20026 and so on).
   How plausible does this sound?

2. Can multiple instances of the server (say, from my previous
   example, Netscape) coexist in one host? Obviously I'll need
   to specify different config files and different spool locations,
   but that's easy; any catch that I may be missing? Does anyone
   have experience with running multiple Netscape Messaging Server
   instances in one host (preferrably, in an application proxy
   border zone)? Might there be some hidden global serialization
   lock that will not let multiple instance run, after all?

Or am I being completely stupid and current crop mail servers
can do multiple domains over multiple repositories? I couldn't
find this in online documentation that I browsed.

Thank you in advance!
Doron Shikmoni