Add 2 way Relay email like on craigslist. CodeIgniter. Jquery. Java. Google Maps API

Need the 2 way email relay set up like on craigslist. Example for both senders: [login to view URL] [login to view URL] Each sender has confidential emails. So far it has been set up on the site, and uses cron jobs. But the email format received is messed up, and very rarely emails are not going through. Also this is currently working for registered users only. Needs to work for users not logged in as well, that input their email in the reply form.