Question

In the App Engine “Application Settings” page it lists an email address:

[e-mail]

If someone sends an email to this address, how do I read it?

What do I need this address for?

Answer 1

I don’t think it is an email address. This is the service account name, an external identifier for your application.

The settings page says:

Use this name when interacting with external services on behalf of
your application.

You use it e.g. while connecting your app to Google Cloud Storage.