This proved useful when I implemented MailScanner for Carbide-Finger Limited

By adding a smart router you can act as the primary mx for a domain that actually isn't local to your server at all for example: I used this to push virus & spam filtered mail onto a customers Exchange Server negating the need for POP boxes.

To implement smart routers:

touch /etc/staticroutes

Then open /etc/staticroutes in your favourite text editor (vi is my preference) and add each domain you would like pushed on in the following format (one per line):

domainname.com: target.mail.server

target.mail.server can be a FQDN or an IP address

In the Routers Configuration section of your exim.conf add the following:

static_route:
   driver = manualroute
   transport = remote_smtp
   route_data = ${lookup{$domain}lsearch{/etc/staticroutes}}

Then after an exim restart you should have working smart routers (its always worthwhile to tail the exim_mainlog for a while afterwards just to make sure its ok)

service exim restart

Thanks to 'projectandrew' on the cPanel Forums for this one.

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