Best practice is to use namespaced claims to avoid any sort of name collision. The namespace could be your own domain for example. If you have good reason you can now leave off the namespace but follow these guidelines https://auth0.com/docs/secure/tokens/json-web-tokens/create-custom-claims#non-namespaced-guidelines
So you’ve created a Post Login Action and are adding email from the user profile to the Id Token but you cannot find it in your application when logging in?
Try putting some console.logs in your Action to ensure it’s executing and inspecting variables and use the Real-time webtask logs extension to view the output of those logs.
If you’re happy it’s executing try looping through the claims in your app post login to check it is there.
Warm regards.