The email address of a Discourse user is sensitive enough that it’s not shown by default, and the act of an Admin seeing it is logged.
When importing users (at least using the MyBB importer), the user’s name is derived from their email address. Since a lot of users use a small set of popular email providers (Gmail, Yahoo! etc.), this has the effect of leaking the user’s email, not just to the admin or other forum users, but to anyone on the Internet: