Hello,
Have you read the post I sent you? I did not tell you that somebody used your domain. I told you that if users on your site change the pass, create user etc WP sends the default message to WP owner. And that message has the default address – wordpress@site_domain. Please, read the post https://www.wpbeginner.com/plugins/how-to-change-sender-name-in-outgoing-wordpress-email/ attentively to sort out what I’m talking about.
Also, I repeat you that we changed the username to des…..in. I did not want to mention this without private content and added this username to private content area of your previous messages but seems you don’t understand my messages above.
Regards