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When I compare those I get like 3640 active 2013 alumni, and 18 inactive 2013 alumni. I don't see any reason it should not be 100% active, and I think there's a subtle bug in the way Fred wrote the alumni check. I think this needs a slight amount of work to be correct.
How to ingress fake mail to TEST
It is possible to ingress fake mail to TEST, but the process is a lot of effort for low return. Basically, the way you do this is you send mail to PROD service now as the user you want to emulate, then you copy and paste the received message details from PROD service now into TEST service now, then tell ServiceNow to 'process message' on the fake received mail you created manually in TEST. Does that sound hard? It is. Verifying the user detail is a sufficient test of this bug.