On the email administration page for their domain, many customers have a so-called "catch-all" address. This address function catches all emails sent to your domain, no matter what is entered before the "@".
In order to reduce spam, virus and emails addressed to others, e.g. email@example.com or firstname.lastname@example.org, create unique forwardings for each email address, hence create email@example.com, firstname.lastname@example.org, email@example.com etc.
Remember to also add an address for firstname.lastname@example.org.