Here is what I am trying to do:

Setup an Exim Smart router that checks the local mail users list first, then does the smart route.

I have setup the smart router to forward all mail for 2 domains to our mail server on site, but the problem i am running into is that the smart router does not check for non-existent email addresses therefor there is lots of wasted bandwidth here.

Basically i would like an email to come in, be checked agains the local account list, then shoot a 550 NDR if the account doesnt exist, and deliver if the account does exist. I did find on the cpanel forums where you can have a condition to have the mail spam scanned before delivering, but nothing to check agains local mail accounts.

Thanks in advance.