Suppose you want all mail that arrives at nonexistent mailboxes in your domain to be delivered to a specific mailbox.
For this:
1) On the cPanel main page, in the “Email” section, select “Default Address ”
2) In the window that opens, select the domain (if there are several), select “Forward to Email Address” and specify which address to forward.
Instead of sending it, you can also choose to delete emails, forward to a system mail account, or send to a script.
Done.