Load Balancing SMTP Traffic

I would like to ask about load balancing SMTP traffic.  We are designing our Exchange 2010 deployment and will be using a netscaler to load balance CAS traffic (OWA, EAS, etc..).  Another question that was asked is whether or not we should be load balancing SMTP traffic?  Currently we have a hosted spam solution that after filtering email sends the message to our HT server.  For 2010 we were thinking of load balancing this and having external email sent to the Netscaler which in turn would handle delivery to the HT servers.  My only concern is since the source IP would be showing as the netscaler and we would need to put the IP pf the VIP in the allowed relay section of the receive connector we in fact would be doing an open relay.. = very bad!

My question is.... is there a way I can do load balancing for SMTP without having this issue?  The only other option would be for our spam service to send directly to the HT servers which then requires those servers to have a public IP which I really dont want to do.  

Thanks.... this is the article I have been reading all day and trying to comprehend

http://exchangeserverpro.com/issues-with-load-balancing-smtp-traffic/