One reason might be that we updated the servers to Exchange 2013 CU7 as part of the move, another reason might be that we updated pfsense from 2.0.2 to 2.1.5, but basically what used to work for Exchange 2013 CU3 and pfsense 2.0.2 no longer works in these later versions.
Server Load Balancing | pfSense Documentation Aug 06, 2019 Server Load Balancing — Web Server Load Balancing Example Feb 07, 2019 How To Use pfSense To Load Balance Your Web Servers
Server Load Balancing and Failover - pfSense Hangout
Load balancing avec PfSense | SUPINFO, École Supérieure d
Configuring multi-WAN load balancing - pfSense 2 Cookbook
Inbound load balancing is used to distribute load between multiple servers. This is commonly used with web servers, mail servers, and others. Servers that fail to respond to ping requests or TCP port connections are removed from the pool. Virtual Private Network (VPN) The pfSense software offers three options for VPN connectivity, IPsec