d8mail.module

<?php

use Drupal\Component\Utility\SafeMarkup;

/**
 * Implements hook_entity_insert().
 */
function d8mail_entity_insert(Drupal\Core\Entity\EntityInterface $entity) {

  if ($entity->getEntityTypeId() !== 'node' || ($entity->getEntityTypeId() === 'node' && $entity->bundle() !== 'article')) {
    return;
  }

  $mailManager = \Drupal::service('plugin.manager.mail');

  $module = 'd8mail';
  $key = 'node_insert';
  $to = \Drupal::currentUser()->getEmail();
  $params['message'] = $entity->get('body')->value;
  $params['node_title'] = $entity->label();
  $langcode = \Drupal::currentUser()->getPreferredLangcode();
  $send = true;

  $result = $mailManager->mail($module, $key, $to, $langcode, $params, NULL, $send);
  if ( ! $result['result']) {
    $message = t('There was a problem sending your email notification to @email for creating node @id.', array('@email' => $to, '@id' => $entity->id()));
    drupal_set_message($message, 'error');
    \Drupal::logger('d8mail')->error($message);
    return;
  }

  $message = t('An email notification has been sent to @email for creating node @id.', array('@email' => $to, '@id' => $entity->id()));
  drupal_set_message($message);
  \Drupal::logger('d8mail')->notice($message);
}

/**
 * Implements hook_mail().
 */
function d8mail_mail($key, &$message, $params) {
  $options = array(
    'langcode' => $message['langcode'],
  );

  switch ($key) {
    case 'node_insert':
      $message['from'] = \Drupal::config('system.site')->get('mail');
      $message['subject'] = t('Node created: @title', array('@title' => $params['node_title']), $options);
      $message['body'][] = SafeMarkup::checkPlain($params['message']);
      break;
  }
}

/**
 * Implements hook_mail_alter().
 */
function d8mail_mail_alter(&$message) {
  switch ($message['key']) {
    case 'node_insert':
      $message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed; delsp=yes';
      break;
  }
}