My mail server is set up so that every email to the domain comes to me. One can email firstname.lastname@example.org, and it will forward to me.
I often get spam to strange address. Let's say, Bob_White@mydomain.com - just random names. I get a lot of these, always to different names. On any other mail server, the invalid address would just bounce back to the spammer. So why am I getting spam to these addresses?