How to go about setting up F5 as SMTP relay for outbound (not inbound)

I want to setup my CAS array (NLB) send connector going to the BIP-IP LTM as a virtual IP, what else must i configure to route the SMTP traffic outbound. Must the Virtual server members be the external mail servers ? Can it work in this configuration to replace a Symantec Messaging Gateway, obviously two different appliances i understand, but more so just sending outbound mail across i want to load balance the SMTP going outbound from the connector.

Thanks for your answers.