I saw someone also mentioned about this but there was no solution.
Under WHM, I restored a *.tar.gz file and re-created an old account. After that, I changed the domain from olddomain.com to newdomain.com.
Under cPanel of that account, it shows me:
firstname.lastname@example.org (which was added before the account was deleted earlier)
email@example.com (which I just added)
I tried to delete firstname.lastname@example.org but it said I have no access to this domain.
I checked httpd.conf and there was no occurrence of olddomain.com.
How do I manually remove this old email account?