I have a split domain architecture and have configured
Zimbra as the Secondary System per the wiki page.
I would like all messages from zimbra users to
route via the legacy mta (to receive anti-malware service
based on that customized gateway system and to
obtain other facility services at the relay). Outgoing messages
to addresses without zimbra accounts do go to the
relay mta for external delivery as desired. But I also desire
addresses with zimbra accounts to also route via the
relay mta (which will then forward them back with the
server name address format).

The legacy mta has the mx record for the zimbra domain named on the
zimbra server and in all other respects things are working as desired.
I just want to add external routing for local zimbra address messages.

I expected changing the zimbraMailCatchAllAddress and
zimbraMailCatchAllForwardingAddress states to "" might
allow messages route out in this way, but messages remained
locally delivered.

I seek suggestions on how I might architect this.

zimbra server dns zserver.dept.example.com
holds zimbra domain dept.example.com
The mx to dept.example.com points to mail.dept.example.com

If zimbra user user1@dept.example.com sends to
self or another zimbra account, say to self as user1@dept.example.com,
I want it to route via the mx lookup to mail.dept.example.com,
which will then route it back as a known zimbra user to
user1@zserver.dept.example.com. Unfortunately, in my present
configuration, it does local delivery of all existing accounts without
using the relay mta.
after following the split domain guidance I then tried
zmprov md dept.example.com zimbraMailCatchAllAddress ""
zmprov md dept.example.com zimbraMailCatchAllForwardingAddress ""
but that didn't "uncatch" the locals.