The following are the procedure to Blacklisting Email in cPanel.
Log in to your cPanel account and search for Spam Filters.
Enter Spam Filters.
Go to the section "Additional Configurations (For Advanced Users)" click on the "Show Additional Configurations" option. Then click on the option "Edit Spam Blacklist Setting".
Go to the Add A New “Blacklist_from” option. Then a new box will open. You can enter the email address you want to blacklist in cPanel on the new tab and click on "Update Blacklist (Blacklistlist_from)".