[Plugin: AJAX Quick Subscribe] E-mail to admin when new user subscribed?

To send an email to admin when new user subscribes, you need to add the function into ajaxQuickSubscribe.php in the plugins folder.

the function is:

wp_new_user_notification($user_id);

Look for line 111:

$user = new WP_User($user_id);
$user->set_role('subscriber');

and change to:

$user = new WP_User($user_id);
wp_new_user_notification($user_id);
$user->set_role('subscriber');

If you want to also email the subscriber (although I see no point in this) then change:

wp_new_user_notification($user_id);

to:

wp_new_user_notification($user_id, $user_pass);