Hi @Gökay Kazdal ,
I suppose you have the mail handler set up in your Jira. You need to go to the mail handler configuration (System -> Incoming mail -> Edit the mail handler which creates the issue in the mentioned project) and check if the Default Reporter is set to empty. If not, you need to clear it.
However, be aware that if the person, who sends the email does not have the account, the email will be ignored, unless you have "Create users" checked.