EXBPA states that one NIC is not active. In fact, I only cabled one of the two NICs. Would I gain anything from cabling both NICs? In theory? In practice? We have less than 150 users, most of them light users 5-10 emails sent/received a day.

It is best practice to disable any nics that you are not using. You could cable the other nic and "team" the two nics for fault tolerance.Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com

It is best practice to disable any nics that you are not using. Yes, that's what I did (used to get error messages about that, so I just disabled it). You could cable the other nic and "team" the two nics for fault tolerance. Would there be any advantage (or disadvantage) to connecting each NIC to a separate switch? (Working with VMWare vSphere/ESXi in my spare time and I see that each host is connected to two different switches with, from there, two connections to a distinct port on the SAN device) I don't know if the same logic applies - at any level - here. No, I do not use shared storage with Exchange (the vSphere comment was a simple comparison - only used for play... I mean practice)

Yes it would be an advantage to configure the nics in a fault tolerant fashion. Make sure that your switch and netowrking software is capable of that. In this set up, if a switch failed or nic failed your Exchange server would still be functional.Tim Harrington - Catapult Systems - http://HowDoUC.blogspot.com

The Nic which is not active should be lower in the Nic card bindings, if you have disabled that or are not using the Nic. Make sure the active Nic is on the top of the binding order.

I just made sure active NIC is at top of bindings (it was not). That change also seems to remove the warning from the EXBPA results (it's no longer there, can't imagine it's a coincidence).