Hi If you don't want to receive any copies of the emails sent to an address @yourdomain, the best would be not to create the mailbox in your cPanel in the first place OR delete the mailbox from cPanel if already created (create backups if necessary).
Then go into cPanel and setup a forwarder for the mailbox and forward it to the desired address, this is essentially setting up an Alias for that mailbox. It doesn't exist as a physical mailbox, but simply redirects those emails to the other address.
Example of when I would use this: I want the following addresses - sales, info, accounts firstname.lastname@example.org all to forward emails to my existing address @gmail.com I don't wish to setup all these mailboxes on my computer and I don't want them to receive any emails, all they must do is forward all emails sent to them, to my @gmail.com address.
Add a forwarder: Clientzone login > Hosting > Select domain > Login to cPanel > Forwarders > Add forwarder Add/remove mailbox: Clientzone login > Hosting > Select domain > Login to cPanel > Email accounts > Create account