Under what circumstances can a user’s email address result in uppercase characters?
Email addresses are always normalized to lowercase for users in Auth0 database connections. This includes passwordless.
If import mode is enabled, Auth0 is the source of truth for users with the external database as a fallback for those not found. The result is that all email addresses will be normalized to lowercase. If import mode is disabled, however, the external database is the source of truth; therefore, the email address can contain uppercase characters.
Email addresses can contain uppercase characters when the user is sourced from an external identity provider, i.e., a non-Auth0 connection such as an enterprise or social connection.