1. Log into your cPanel, navigate to Email section > Forwarders:
2. To create a new forwarding rule, click on Add Forwarder:
3. Fill out the fields and when ready click on Add Forwarder:
NOTE: You can forward emails sent to the non-existent mailbox without having to create the mailbox itself.
If you would like to set up catch-all, you can use Default Address menu:
The default email address will 'catch' any mail that is sent to an invalid email address for your domain.
So if you would like all email sent to @yourdomain.com to be forwarded to existing mailbox email@example.com, the forwarder should look as follows: