We're migrating from an iPlanet (SunOne) ver. 5.2 emai/calendar system to
Zimbra (latest network version.) We'll be running a split domain with iPlanet as the primary server and zimbra as the secondary.
Currently email routing for * through the zimbra MTA seems correct. If the user is found locally, email is delivered to zimbra and if not, it's forwarded to iPlanet and if the user is found, delivered there.
My question/issue/problem is that we're going to adjust the forwarding
address of our migrated, iPlanet users to the newer Zimbra MTA for delivery
from the other direction. However we get a bounce sending mail to and it simply bounces back. (Note: zmta is the name of our zimbra mta host.)
Can I or Should I create a "domain alias" for such as "" so that our forwards from the old system to zimbra can get through cleanly? If I use the hostname of the zimbra mta server postfix tries to deliver the mail locally. An aliases file on the mta requires local accounts be created and that's out.
Any thoughts or help would be great,

OS: RedHat ES 4. whatever's the latest
Zimbra: 4.0.4 Network Edition (latest also)

iPlanet config: (single box, web,imap,pop,smpt,cal)

Zimbra config: (store, logger, web, imap, pop) (Zimbra LDAP) (Zimbra MTA, AV, AS)