Does "credentials@stanford.edu" usually not reply to emails?

[skieurope]

I’m not sure what you expected them to say. Even if the email was not a non-reply address, not all emails warrant a reply. This statement applies to all college admissions offices.

Regardless, Stanford answers the question for you:

Please note that we are unable to confirm receipt of optional materials that are not required for admission. These materials are not tracked in our system.

https://admission.stanford.edu/apply/freshman/evals.html