The easiest way to make your site a spam source (anyone can cause anyone else to receive email they don’t want–this happens to people I know with some frequency) and target (you don’t know that the people who are logging in even have an email address) as you desire is to use some other authentication system, like Wordpress, and make it be the DiscourseConnect server. You can configure WordPress not to validate email addresses and add some code to your functions.php that will tell Discourse that the email addresses have been validated (See “Remove the require_activation flag” in the link below).
See Configure single sign-on (SSO) with WP Discourse and DiscourseConnect