[Exim] Email gateway server setup

Hi,

We would like to configure one email gateway server for all incoming and
outgoing mails.
Following is added to internal SMTP server.

send_to_gateway:
      driver = manualroute
      domains = ! +local_domains
      transport = remote_smtp
      route_list = * 202.179.0.xxx

Following is added on Email gateway.
hub_route:
     driver = manualroute
     transport = remote_smtp
     route_list = +remote_hosts 202.179.0.xxx
     no_more

The idea is email gateway receives all mails those destined to internal
hosts and sends all mails from internal hosts to those destined not for
local domains.
Each host has virusscan with exiscan and everytime when I send email to
other domains exiscan checks viruses and adds extra header info. This way
every email has 2 exiscan X-scanner header line.

How to eliminate duplicate checking?

Also how to setup authentication between these Email gateway and internal
SMTP servers?

What will happen if email gateway server will fail accidentally? Is there
any configuration for this?

What should I do if I want to configure internal servers to send all mails
to Email gateway server? I tried without

domains = ! +local_domains

line but it keeps bouncing back and forth because gateway server sends it back.
Any suggestions?


TIA,

Ganbold