The mail server we are attempting to replace fully with a ZCS 4.0.1 Network Edition server performs email filtering for a few of our clients' domains. On that server, Postfix is configured with transport maps and relay domain entries. That server is the MX for those clients' domains, so that server receives mail, filters it through amavis, and then relays it to the clients' mail servers (which are Exchange boxes with a public IP but no A nor MX record in public DNS). That server has no cyrus mailboxes for any of those clients' users. It's just mail in, scrub it, and send it on its way.

If we can configure this functionality on our Zimbra server, then we can fully decommission that other server.

Are Postfix relay domains a supported configuration on the Network Edition?