Create an alias in the admin panel … (using the API)
But this is not the recommended approach as some providers (looking at you Goofle) do not respect SRS. And many other email providers (such as Yahoo!) do not allow for their emails to be forwarded - meaning that receiving servers bounce them.
https://mxroute.com/google-does-not-respect-srs-do-not-forward-email-to-google/