How to use same email for multiple users in Multisite version 4.7

Question

I tried the code listed in this answer, and this allowed me to create 2 users with the same email address, but not a third.

add_filter('wpmu_validate_user_signup', 'skip_email_exist');
function skip_email_exist($result){
    if(isset($result['errors']->errors['user_email']) && ($key = array_search(__('Sorry, that email address is already used!'), $result['errors']->errors['user_email'])) !== false) {
        unset($result['errors']->errors['user_email'][$key]);
        if (empty($result['errors']->errors['user_email'])) unset($result['errors']->errors['user_email']);
    }
    define( 'WP_IMPORTING', 'SKIP_EMAIL_EXIST' );
    return $result;
}

When trying to create a third user, I receive the error message:

That email address has already been used. Please check your inbox for an activation email. It will become available in a couple of days if you do nothing.

even though I checked "Skip Confirmation Email".

I've also tried the plugin Allow Multiple Accounts but this fails when creating the 3rd user account with the same email address too.

How can I allow more than 2 users to be created with the same email address in Wordpress >4.7?

Answer 1

Depending on which email provider you use, the easiest way is probably to use the [email protected] format. Many common email systems will deliver mail as though it were addressed to [email protected]. The +tag portion of the email address can then be used both for filing mail and for screening it. WordPress, however, will see it as a different email address.