I've setup a Rule to send emails containing specific type of Invoices (INV::xxx) to another user

the user is NOT a GW user and I get

The message that you sent was undeliverable to the following:

chris@anotherdomain.com (554 5.7.1 <>: Sender address rejected: Access denied)

Tried this suggestion https://www.novell.com/support/kb/doc.php?id=7012862 to put IP of the Internal GWIA server but still not working
any ideas ?

Works fine if Internal GW user