Maintain Client IP on LTM for SMTP - Involves multiple subnets
I have two SMTP (Exchange 2010) servers that need to be load balanced and maintain client IP for ACLs on multiple receive connectors. So I've disabled SNAT on the virtual server and set the gateway of the servers to the self IP of the LTM. That works great, I telnet to the vIP and the load balance works fine, EHLO shows my IP and not the self IP, all is well.
The problem comes when trying to make a direct connection to either of the servers from outside the subnet they're on. My client's environment is quite large and consists of about 150 VLANs and the same amount of subnets. Lucky for me about half of them need to make direct connections to these servers. Another problem, is that these servers need to connect to the internet to send e-mail out, not through the LTM, and they can't do this when using the self IP as the gateway.
Now, the LTM was added late in the picture of their network, so it's side-armed in the network and not in-line. Adding it in-line is also not an option. In other words, the LTM is plugged into the same switch(es) that these servers and the router are plugged into.
What are my options here, if any? Thanks for any help!