Email Subscribers When a New Post Is Published

$wpide_announce = array(
    'role'       => 'subscriber',
    'post_type'  => 'post',
    'batch_size' => 50,
);

add_action( 'transition_post_status', function ( $new, $old, $post ) use ( $wpide_announce ) {
    if ( 'publish' !== $new || 'publish' === $old || $wpide_announce['post_type'] !== $post->post_type || get_post_meta( $post->ID, '_wpide_announced', true ) ) {
        return;
    }

    update_post_meta( $post->ID, '_wpide_announced', time() );
    wp_schedule_single_event( time() + MINUTE_IN_SECONDS, 'wpide_announce_batch', array( (int) $post->ID, 0 ) );
}, 10, 3 );

add_action( 'wpide_announce_batch', function ( $post_id = 0, $offset = 0 ) use ( $wpide_announce ) {
    $post = get_post( (int) $post_id );
    if ( ! $post || 'publish' !== $post->post_status ) {
        return;
    }

    $emails = get_users( array( 'role' => $wpide_announce['role'], 'fields' => 'user_email', 'number' => $wpide_announce['batch_size'], 'offset' => (int) $offset, 'orderby' => 'ID' ) );
    if ( ! $emails ) {
        return;
    }

    $site    = wp_specialchars_decode( get_bloginfo( 'name' ), ENT_QUOTES );
    $excerpt = wp_trim_words( wp_strip_all_tags( $post->post_excerpt ? $post->post_excerpt : strip_shortcodes( $post->post_content ) ), 50 );
    $headers = array( 'Bcc: ' . implode( ',', array_filter( $emails, 'is_email' ) ) );

    wp_mail( get_option( 'admin_email' ), sprintf( '[%s] New post: %s', $site, wp_strip_all_tags( get_the_title( $post ) ) ), $excerpt . "\n\nRead more: " . get_permalink( $post ) . "\n\nYou receive this because you have an account on $site. Update your preferences: " . admin_url( 'profile.php' ), $headers );

    if ( count( $emails ) === $wpide_announce['batch_size'] ) {
        wp_schedule_single_event( time() + 2 * MINUTE_IN_SECONDS, 'wpide_announce_batch', array( (int) $post_id, (int) $offset + $wpide_announce['batch_size'] ) );
    }
}, 10, 2 );