cPanel by default creates an email account same as cPanel’s username. It is not possible to delete this email account and it may be used by cPanel internally. Also, you will see cpanel_user@servername when you send emails via script.
Also, if default account (catch-all) is enabled, all your unrouted emails for your domains will be delivered in this account. This is a default settings in cPanel. It is not recommended to keep default email account (catch-all) account because it can cause disk space issue as well as it increases the server resource usage.
If you wish to disable default email account (catch-all account), you can refer Disable catch all / default email address in cPanel / WHM forum thread.