I have a Drupal 7 website in Ubuntu 12 on a VPS machine. So I’m responsible for getting email working on my own.
This page has good instructions on setting up Postfix:
tail -f /var/log/mail.log to watch the progress of mail sent from the Drupal site.
If the the site is example.com and you’re mailing to firstname.lastname@example.org, you want to see log entries like this: