Jeff,
You can use “last receive” as Alert Type for the IB thread like this.
Trigger:
Alert Type: last receive
Source: IbThreadName
Source Count: all
Comparing: >=, 1
Duration: N min…, 600
Time Window: * * 8-18 * * 0-6
Then in the Action tab, you can use an exec to send a mail or just do a notify.
Hope this helps,
Sam