Require confirmation on email change

[linuxologos]

When a new user is registered for a site, the e-mail he provides gets easily confirmed. But immediately after that, the new member can visit his profile and is able to change his e-mail to anything. Regardless of whether it is done on purpose or the user enters a wrong e-mail by mistake, the admin cannot contact the member, should he has to for any reason. The e-mail address is of great importance in such cases and I don't think that's a rare need!

I've had the impression that WP was not offering this feature, but then I realised that the code lies in core, though restricted to multisite installations. I find it quite difficult to understand why.

There might seem to be a relation to #13717, but what I propose hereby is just giving the admin of a single-site installation the option to activate e-mail change confirmation.

I think the implementation would only require a few changes in wp-admin/user-edit.php, making send_confirmation_on_profile_email() available outside of wp-admin/includes/ms.php and adding an option in Settings.

Why would we have to hack the core or consider a plugin for something almost already offered in core? That's why I describe the ticket as "enhancement", not "feature request".