You can't have an anonymous relay and require auth on the same connector. Those are two opposing concepts.
Exchange 2016 Authenticated Relay
I am using an old Exchange 2016 Server as an internal SMTP relay for things on-prem that don't play well with O365.
I am trying to configure a connector so that it requires authentication but acts like an anonymous relay.
Example, upon connecting from anywhere, you do the usual SMTP auth but at the point where you enter the from email address you can put anything.
At the moment it requires the from address to be the one that is listed on the authenticated users AD account.
I have already tried adding the ms-Exch-SMTP-Accept-Any-Sender permission manually to the connector but still no joy.
Can anyone suggest anything?