In WHM I had emails to nobody and cpanel under “Edit System Mail Preferences” setup to go to root but nothing specified for root.
The setup basically became confused and I was stuck with thousands of frozen emails to root@hostname emails in Exim hogging the email queue.
You can quickly and easily find and remove all frozen emails in the Exim queue with ease. See the command and then the link below.
exim -bp | grep -c frozen