email examples for a newbie

[Jimmy Brake]

Hi,

Can someone point me towards or send me an example of smtp proxiing(or 
let me know that nginx will not do it)?

Scenario:

A single server running nginx on port 25. Emails to jimmy at demo.com get 
delivered to server 192.168.0.5.
Emails to alberto at demo.com get delivered to server 192.168.0.4

Thanks,

Jimmy