cPanel email offers two options for email forwarding:
Forwarders send a copy of every email received at an address to another address. For example, setting up a Forwarder for firstname.lastname@example.org, forwarding to email@example.com, Jane will receive a copy of every message sent to John.
Forwarders in cPanel work even if the forwarding email address doesn't exist. In the example above, even if firstname.lastname@example.org didn't exist as its own email account, email@example.com would still receive emails sent to John.
Forward All Email for a Domain forwards any email sent to a domain name to the same email address at another domain name. For example, if you forward all email for coolexample.com to coolexample.net, all email sent to firstname.lastname@example.org gets forwarded to email@example.com. For more information, see cPanel's documentation.
If you Forward All Email for a Domain, that domain's email addresses do not receive email.