So I have some custom VPS which route emails via MX record in DNS. And I need to setup gmail interface via Google Apps - this step and previous are clear. But how can I insert some middle layer, to check emails messages for special words/etc., so something like spam assasin proxy, but custom product.
The question is: How could i setup proxy mail from my server => to proxy server(or application) => to gmail servers?
Thank you, for any help!