Disable Emails v1.8.0 has just been released. With this release, the mock PHPMailer object now records recipient addresses for developers to inspect.
Whilst sending emails is blocked by the plugin, it all still needs to look like emails are working so that other plugins don’t get nervous. To that end, email recipients added to an email are properly recorded on the mock PHPMailer object so that other plugins can inspect them.
You can update to the latest version from your WordPress plugin admin page. Here’s the full changelog for Disable Emails.