Thank you very much for the quick reply. I hadn't considered the consequences of blocking India vs India_Rep.
It turns out that entire subnet is controlled by Cisco and several of our Texas state counties are assigned IPs in that range. Since this "problem" only began after July 2nd (the last time they were able to connect to our mail server using that same IP), we assumed it was entered by mistake.
I've informed our customer and they will get with Cisco to determine a resolution, as it seems they're also now being blocked by other mail servers as well as their hosted helpdesk app is failing. All of these problems began sometime after July 2nd, which is when I assume the IP was entered into the India_Rep database.
Thanks again for your assistance!
David