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

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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
Not sure where you have got the idea that you will be an open relay.
I presume you have a list of IP addresses from the external antispam service? If so, configure your firewall to only accept SMTP traffic from them. Send the traffic to the netscaler and configure the receive connector to only accept email from the netscaler. At no point does that turn you in to an open relay (unless you have changed something else in the recieve connector configuration).

mkllpitAuthor Commented:
Thanks Simon!  I actually thought about that on the way home and it makes perfect sense!
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