A spammer can send spam emails to "firstname.lastname@example.org", and Postfix will created a new directory /var/mail/mail to hold the emails. This has happened a couple of times before with similar names. For example, a spammer sends an email to "email@example.com", and when I look at Ubuntu, I see a new directory /var/mail/test has been created to hold the spam emails.
How can I prevent this? Di I have Ubuntu configured wrong or Postfix or both?