My issue:
I have a zimbra server, and a regular postfix server. Zimbra is becoming the primary, and during migration trying to keep postfix as secondary. I am trying to migrate a few people at a time, and trying to use the split domain setup. What my go is to try to send emails to a "fake" domain on zimbra using zimbra users that exist, and forward to users that do exist to the old postfix server.. fake-domain and postfix-domain have the same name.... So I tried this:

zmprov md fake-domain.com zimbraMailCatchAllAddress @postfix-domain.com zimbraMailCatchAllForwardAddress @zimbra-domain.com zimbraMailTransport smtp:mail.postfix-domain.com:25

My understanding from the split domain doc that users that exist on zimbra will receive mail, but users that do not will be forwarded to the postfix-domain where they actually do. But, I immediately get a bounce back saying (to a postfix-domain address...

This is the mail system at host zimbra.zimbra-domain.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<user@zimbra-domain.com>: zimbra-domain.com


Any ideas?? It works perfectly fine for people sending in externally. But users within zimbra cannot send over to users on the postfix server. Thanks in advance