If you want to have a copy of each email you receive, to be sent into another email address, then the Mail flow is where you can set that option; here is how:
-Open Mail Flow tab
-Select Enable Forwarding
-Click on Lookup User
-A list of users will open up where you can select the user you want.
-Select Deliver message to both forwarding address and mailbox so that both emails can receive the message.
Note: If you want to add an email that is not listed in the mailbox as it’s using a different domain, then you can add it to the contacts so that it will be shown here in the list.
Please check how to add contacts from the listed menu.