If you want a particular E-Mail address to mail to multiple inboxes (a forward to two or more addresses), just setup a forwarder entry for each address in your cPanel. You can do it one by one, or do all the emails separated by a comma i.e. firstname.lastname@example.org, email@example.com.
Ultimately, you would end up with entries such as those below.
firstname.lastname@example.org -> email@example.com
firstname.lastname@example.org -> email@example.com
firstname.lastname@example.org -> email@example.com
This is done by going to the Mail Section within cPanel and clicking on Forwarders.