As a victim of harassment, I may not want my email address disclosed every time I use Special:Emailuser. Github has a setting "Keep my email address private" that sets all publicly facing email addresses (e.g. in commit metadata) to, say, MER-C(at)users.noreply.github.com. A preference should be added to MediaWiki that, when enabled, sets all emails sent via Special:Emailuser to have a sender of, say, MER-C(at)no-reply.wikimedia.org. All emails sent to this address would be discarded silently.