How to resolve Drupal unable to send email - contact the site administrator?

In earlier versions of Drupal or for that matter even WordPress, the site could send email notifications easily using the PHP mail function. However, most hosts have disabled the default mail function due to security and vulnerability reasons. Therefore, emails will not go. This is not a Drupal issue as the same  issue we see on WordPress as well. In this post, we shall discuss how to let Drupal site send out emails using a third party module.