WP: Email Users On Post

email_on_post.php

<?php
	function email_members($post_ID)  {
	    global $wpdb;
		
		// fetch the list of users registered
	    foreach( $wpdb->get_results("SELECT user_email FROM $wpdb->users;") as $key => $object) {
		    $user_emails[] = $object->user_email;
	    }
	    
		$users = implode(',', $user_emails);
		$subject = "";
		$message = "";
		$headers .= 'From: ' . "\r\n";
	    mail($users, $subject, $message, $headers);
	    return $post_ID;
	}
	add_action('publish_post', 'email_members');