Found out information:
Inbound Traffic Flow Sender --> McAfee MX --> Google Apps MX --> My Inbox
Outboud Traffic Flow My Outbox --> Google Apps SMTP --> SMARTHOST --> Recepient
Clients do not need to be reconfigured.
As for the Inbound and Outbound server configuration
Inbound Server - Type in the MX record of your domain name (if this is for your email protection), or your customer's domain (if you are providng MSP)
The inbound server is where McAfee will send your messages after they have been filtered.
Outbound Server - Type in the SMTP Address to your domain, or your customer's domain.
Normall your put in the SMTP server for your smail organization here. Google Apps is different and according to support, you just need to check the box and save it.
If you do want to encrypt your outbound mail and filter it, you should setup a smart host with your email provider, this will relay messages sent from you, throug McAfee's server for check and wrapping before it goes to the customer.
Hope this helps everyone.