We have a lot of old emails that are using an image URL with http instead of https. The image automatically redirects to https if you load it in your browser, but it still appears in these old emails that are using the http link. Is it possible to disable the http URL so the image won't load in emails that use the http URL? Or is it possible to force all the email assets using the http URL to update to the https URL? There are over 12,000 emails using the asset and they'll need to be manually updated, so it's not really feasible.
The answer is no, an admin can’t disable the plaintext endpoint so the http:// URL will still work. But why would you want to deliberately break images?