Send email when a post is sent for review (pending) in WordPress

Here’s a quick snippet for sending an email when a post is sent for review. (Post status: Pending) This happens when a Contributor writes a post. Since they don’t have the publish_post capability, their post will have the status of “pending”. (Do you want to send email when a new post is published? Read this post instead!)

add_action('future_to_pending', 'send_emails_on_new_event');
add_action('new_to_pending', 'send_emails_on_new_event');
add_action('draft_to_pending', 'send_emails_on_new_event');
add_action('auto-draft_to_pending', 'send_emails_on_new_event');

/**
 * Send emails on event publication
 *
 * @param WP_Post $post
 */
function send_emails_on_new_event($post)
{
    $emails = "email_1@mail.com, email_2@mail.com"; //If you want to send to site administrator, use $emails = get_option('admin_email');
    $title = wp_strip_all_tags(get_the_title($post->ID));
    $url = get_permalink($post->ID);
    $message = "Link to post: \n{$url}";

    wp_mail($emails, "New post published: {$title}", $message);
}    

This will result in an email like this:

[Title] New post published: Your Post

Link to post:
http://site.com/your-post/

If you need to do this for a specific post type only you can have a conditional inside the filter function:

...
if(get_post_type($post->ID) === 'page') //post, page, attachment or whatever other CPT you may have
{
    //use wp_mail() here!
}
...