Your domain has that particular account set as the dump account so that all email to that domain, that isn't routed to a particular email address will also go to that account. It's a mail dump account. You need to access the domain's server settings and have it set to reject all emails that aren't to your defined email accounts.
I have a family domain (let ud say zebra.com
In the inbox of firstname.lastname@example.org you vil find a mail with the receiving mail address of email@example.com
How is this possible ???
All mails are spam mails and Jens is NOT receiving them although it looks as if he was the one that should receive them